This is a very advanced strategy, and since I don't actually have a group to do the full testing with, I'm going off some simulated data.
This requires 4 players, 1 of them being a necro. The other 3 don't really matter.
Group setup:
The group is designed as follows:
The necromancer (The leveler)
The cursed chest finder (class doesn't matter)
2x blood goblin farmers (class doesn't matter)
Vendors to check:
Act 1 Ring Vendor (teleport to Weeping Hollow for quick Access)
Act 3 Ring Vendor (Bottom Right)
Act 5 Ring Vendor (Bottom)
Necromancer skills (equip when available, otherwise, use whatever you're after)
Corpse Explosion: Close Quarters
Blood Rush: Potency
Command Golem: Flesh Golem
Bone Armor: Vengeful Armaments
Bone Spikes: Sudden Impact
Land of the Dead: Frozen Lands
Passive Skills:
Stand Alone
Commander of the Risen Dead
Final Service
Part 1:
Run the challenge cache.
Unless they changed something, as long as you complete the challenge rift after the season starts, you can start ahead of the season. Last season, this didn't work as the season didn't start if you were in the challenge rift, so it may have been corrected. I'll be checking on Asia though when the new season starts.
Start the game with one player who will buy and craft gear for the necromancer (the chest finder). The other two people are searching for blood goblins. When they find a blood goblin, hold it for the necromancer..
Gear to buy:
Act 1: Weapon (preferably with +XP) and the 4 armor pieces.
Gear to craft
Level 5 Axe
Level 5 Phylactery
Level 12 Sword
Then, the non necromancer will exit the game, and search for the 3 following Cursed Chests on T6 (make sure to stay Level 1. You're not to level up at all):
Cursed Spire (best)
Cursed Peat
Cursed Bellows (worst)
You'll have more than enough time to find one of these. Once you find it, just hold the game (stay at level 1!!!)
The necromancer will level up to 22+ (grab the cube or whatever is fastest). When 22+, make sure to reform a game to buy the best vendor gear you can. Total time: ~15 minutes
Hopefully a blood goblin has been found by now, and the necro will have some shards roll Grasps of Essence. The necromancer will cube them, and select them. Then they will join in the game of the chest finder. The chest finder waits at the waypoint. Run the cursed chest. If Level 34+ after this cursed chest, skip the next paragraph.
If the necromancer is below level 34 at this point, both players exit the game. The chest finder will search for one of the following chests
Cursed Spire
Cursed Peat
Cursed Bellows
Cursed Court
Cursed Cellar (do not do on hardcore)
Cursed Temple
The necromancer will enter their own game and buy the best possible gear again (switching skills when necessary, etc.) They'll join the chest finders game and repeat the process. The chest finder waits at the waypoint, and the necromancer will run the cursed chest.
After the cursed chest, the necromancer will be level 34+, and the other player will be level 28+ (depending on the chests found). Total time to get to this point is 20-24 minutes.
Now, the necromancer will hopefully have enough blood shards to roll Custerian Wristguards. If they get them, equip them, and then open up and collect the challenge cache rewards. The gold will boost them to level 54. If not, oh well.
The 3 other players will now run Acts 2, 3, and 5 bounties. It will probably take the necromancer 15 minutes to hit level 70 from this point onwards running cursed chests (Look at the above 6 chests). Make sure to craft a Level Reduce Weapon with at least Life on Hit (required), and preferably Vitality.
With the above steps though, softcore was a similar time, and hardcore would have shaved off 6 minutes.
Without Custerians (depending on the level reduce weapon):
Softcore: ~40-50 minutes to hit 70
Hardcore: ~55-65 minutes to hit 70
With Custerians (depending on the level reduce weapon):
Softcore: ~35-45 minutes to hit 70.
Hardcore: ~40-50 minutes to hit 70.
Once at 70, the necromancer will do the boss kill portions of the bounties, then collect the bounties from their teammates. Runs Acts 1 & 4 bounty sets for the jewelry recipes. Remember that you can purchase 3 jewelry patterns from the Act 2 vendor. The total time to complete the first 4 chapters should be roughly 30 minutes because of your teammates. Then, just power level them to 70. It takes roughly 6-7 T6 bounties to go from level 48-70, assuming they wait in the zone to collect XP. Don't just go to rifts though, get their chapter requirements out of the way for the leveling. At about the 1h45m mark, your entire group should have completed the first 4 chapters and everyone should have their 6 piece. Then, just continue to level up however you want
There are faster group runs out there, so what's great about this?
Well, the person I was playing with, just got Diablo. This isn't a group of 2 expert players leveling to 70. This is me leading both of us to 70, while explaining the strategy to them, all of which was real time. In previous seasons, I've failed miserably when trying to explain leveling strategies the day of the season start. This approach, as long as you learn it, and they can follow a few simple directions of when to join your game, via mic or text chat, can get both of you to 70 in under 75 minutes of the season start. If you have two people who actually practice, and the other player can contribute, below an hour for both players is definitely viable.
The second big factor here is that all you need to gamble are Grasps of Essence. Yes, Bloodtide Blade can get you to 70 faster. But here's last seasons leaderboards at the start of the season:
I was within 10 minutes of the first person to hit 70 on Asia & EU. So, I'm saving Death Breath for when I hit 70, which will help post 70. You have an 86% chance of getting the Grasps of Essence. Even with 4 necros, there's a 30% chance of not being able to get a Bloodtide Blade. Is that difference worth an extra 15 minutes?
Third, the other player can play whatever class they want to, and they don't even need to open up their Challenge Cache for the leveling process.
It's similar to the above start:
Start separate games.
Necromancer:
Gear to buy :
Act 1: Weapon (preferably with +XP) and the 4 armor pieces.
Gear to craft
Level 5 Axe
Level 5 Phylactery
Level 12 Sword
The other player will just search on T6 at level 1 for the following three chests:
Run Temple of the Firstborn on T2 until level 10+. At level 10+, you'll buy +dmg/int rings/amulet. You'll join their game. They'll exit the game. If they found Spire, they'll just wait at the character screen. If not, they'll exit the party and continue looking for a chest, or looking for a better chest. Grab Kanai's Cube. The Elder Sactum is an amazing spot to get a massacre bonus. You're goal is to be level 22+ by the time you grab it. If you're in a game with Spire, or they haven't found a better Cursed Chest, they can join back in to grab it. This part is typically 15 minutes, which is more than enough time to find one of the three chests.
The other player will hold the game with the Cursed Chest, and you'll exit the game to form a new game and buy the best gear you can. I tend to mainly check the Act 1 & 5 ring vendors (and any close vendors to them), which tend to be the fastest ones to reach. Then you'll join the game. They'll wait at the waypoint, and you clear the Cursed Chest. Have them teleport to you after the timer runs out, and while you're still clearing the remaining enemies to speed things up.
Both players exit the game.
The necromancer starts their own game and goes to buy better gear. The other player searches for one of the following chests:
Cursed Spire
Cursed Peat
Cursed Bellows
Cursed Court
Cursed Cellar (do not do on hardcore)
Cursed Temple
Basically, repeat the first Cursed Chest. They wait at the waypoint, teleport near the end to collect loot, you clear the Cursed Chest, etc.
At this point, you two will play separate games until the necro can use their Level Reduce weapon (make sure it has Life on Hit). If under Level 38, run Cursed Chests on T4. If Level 38 or above, play on T3. They'll go grab the cube if they haven't gotten it yet, or just continue to level up however they want while they wait.
When you can use a Level Reduce Weapon, search for Cursed Chests, but now invite them. They'll wait at the waypoint, and teleport when the timer runs out to speed things up, etc. You'll be playing T6 all the way until Level 66. At Level 67+, you'll set the difficulty down to T5. Between every Cursed Chest, both of you should be looking at vendors for the best gear you can. And when either of you hits Level 61+, craft as much Level 61 gear as you can.
When you're Level 70, now both of you will search for Cursed Chests. They'll search on T6 until Level 67, at which point they'll drop to T5. You'll stick to T5(70). And when they hit Level 61+, have them try to start tagging monsters as well for their own Massacre Bonus. For more expert players, they won't actually wait by the waypoint, rather teleport to the necro, and start tagging as well. Provided they stick by the Necro, they should be able to survive. But like I said earlier, this was with a brand new player, so I'm focusing more on a fast working method to 70, rather than a super efficient working way to 70.
Skills:
Corpse Explosion: Close Quarters
Blood Rush: Potency
Command Golem: Flesh Golem
Bone Armor: Vengeful Armaments
Bone Spikes: Sudden Impact
Land of the Dead: Frozen Lands (if they're also tagging)/Shallow Graves (if they're at waypoint)
Stand Alone
Commander of the Risen Dead
Final Service
Some improvements to be made:
First, if you can get the other player to practice this as a necro too, there's a 98% chance of at least one of you getting Grasps of Essence. This significantly beats Bloodtide Blade, where a group of 4 has a 30% chance of not getting it, at which point, their leveling will take far longer. They're basically a backup incase you fail to get it.
Second, if the other player goes after Leoric's Crown, Ring, or Pox Faulds, the leveling will go faster.
Third, if they can use a survivability build to tag monsters, they'll level faster to 70. If they're a monk or barbarian, you can play T6 all the way to 70. And once you hit 70, you're going to be gaining paragon levels anyway, to help with your stats.
This is a very advanced strategy, and since I don't actually have a group to do the full testing with, I'm going off some simulated data.
This requires 4 players, 1 of them being a necro. The other 3 don't really matter.
Group setup:
The group is designed as follows:
The necromancer (The leveler)
The cursed chest finder (class doesn't matter)
2x blood goblin farmers (class doesn't matter)
Vendors to check:
Act 1 Ring Vendor (teleport to Weeping Hollow for quick Access)
Act 3 Ring Vendor (Bottom Right)
Act 5 Ring Vendor (Bottom)
Necromancer skills (equip when available, otherwise, use whatever you're after)
Corpse Explosion: Close Quarters
Blood Rush: Potency
Command Golem: Flesh Golem
Bone Armor: Vengeful Armaments
Bone Spikes: Sudden Impact
Land of the Dead: Frozen Lands
Passive Skills:
Stand Alone
Commander of the Risen Dead
Final Service
Part 1:
Run the challenge cache.
Unless they changed something, as long as you complete the challenge rift after the season starts, you can start ahead of the season. Last season, this didn't work as the season didn't start if you were in the challenge rift, so it may have been corrected. I'll be checking on Asia though when the new season starts.
Start the game with one player who will buy and craft gear for the necromancer (the chest finder). The other two people are searching for blood goblins. When they find a blood goblin, hold it for the necromancer..
Gear to buy:
Act 1: Weapon (preferably with +XP) and the 4 armor pieces.
Gear to craft
Level 5 Axe
Level 5 Phylactery
Level 12 Sword
Then, the non necromancer will exit the game, and search for the 3 following Cursed Chests on T6 (make sure to stay Level 1. You're not to level up at all):
Cursed Spire (best)
Cursed Peat
Cursed Bellows (worst)
You'll have more than enough time to find one of these. Once you find it, just hold the game (stay at level 1!!!)
The necromancer will level up to 22+ (grab the cube or whatever is fastest). When 22+, make sure to reform a game to buy the best vendor gear you can. Total time: ~15 minutes
Hopefully a blood goblin has been found by now, and the necro will have some shards roll Grasps of Essence. The necromancer will cube them, and select them. Then they will join in the game of the chest finder. The chest finder waits at the waypoint. Run the cursed chest. If Level 34+ after this cursed chest, skip the next paragraph.
If the necromancer is below level 34 at this point, both players exit the game. The chest finder will search for one of the following chests
Cursed Spire
Cursed Peat
Cursed Bellows
Cursed Court
Cursed Cellar (do not do on hardcore)
Cursed Temple
The necromancer will enter their own game and buy the best possible gear again (switching skills when necessary, etc.) They'll join the chest finders game and repeat the process. The chest finder waits at the waypoint, and the necromancer will run the cursed chest.
After the cursed chest, the necromancer will be level 34+, and the other player will be level 28+ (depending on the chests found). Total time to get to this point is 20-24 minutes.
Demonstration of the above part: https://www.youtube.com/watch?v=Jg8hMIeJLCg
Now, the necromancer will hopefully have enough blood shards to roll Custerian Wristguards. If they get them, equip them, and then open up and collect the challenge cache rewards. The gold will boost them to level 54. If not, oh well.
The 3 other players will now run Acts 2, 3, and 5 bounties. It will probably take the necromancer 15 minutes to hit level 70 from this point onwards running cursed chests (Look at the above 6 chests). Make sure to craft a Level Reduce Weapon with at least Life on Hit (required), and preferably Vitality.
The following runs were done prior to above step:
41 minute softcore 1-70 run: https://www.youtube.com/watch?v=S1CIxKEsRvI
61 minute hardcore 1-70 run: https://www.youtube.com/watch?v=svdHamCBwDw
With the above steps though, softcore was a similar time, and hardcore would have shaved off 6 minutes.
Without Custerians (depending on the level reduce weapon):
Softcore: ~40-50 minutes to hit 70
Hardcore: ~55-65 minutes to hit 70
With Custerians (depending on the level reduce weapon):
Softcore: ~35-45 minutes to hit 70.
Hardcore: ~40-50 minutes to hit 70.
Once at 70, the necromancer will do the boss kill portions of the bounties, then collect the bounties from their teammates. Runs Acts 1 & 4 bounty sets for the jewelry recipes. Remember that you can purchase 3 jewelry patterns from the Act 2 vendor. The total time to complete the first 4 chapters should be roughly 30 minutes because of your teammates. Then, just power level them to 70. It takes roughly 6-7 T6 bounties to go from level 48-70, assuming they wait in the zone to collect XP. Don't just go to rifts though, get their chapter requirements out of the way for the leveling. At about the 1h45m mark, your entire group should have completed the first 4 chapters and everyone should have their 6 piece. Then, just continue to level up however you want
Season 22 Duo Approach
Rather than the above, this is a more practical leveling strategy.
This is our second ever attempt to get both of us to 70, which took 1h6m: https://www.youtube.com/watch?v=0wBcTTFvTlo
The first attempt took 1h13m: https://www.youtube.com/watch?v=mre-dRJm2ZE
There are faster group runs out there, so what's great about this?
Well, the person I was playing with, just got Diablo. This isn't a group of 2 expert players leveling to 70. This is me leading both of us to 70, while explaining the strategy to them, all of which was real time. In previous seasons, I've failed miserably when trying to explain leveling strategies the day of the season start. This approach, as long as you learn it, and they can follow a few simple directions of when to join your game, via mic or text chat, can get both of you to 70 in under 75 minutes of the season start. If you have two people who actually practice, and the other player can contribute, below an hour for both players is definitely viable.
The second big factor here is that all you need to gamble are Grasps of Essence. Yes, Bloodtide Blade can get you to 70 faster. But here's last seasons leaderboards at the start of the season:
https://i.imgur.com/iUaJbtP.png
The actual leveling time took me 50 minutes on Asia & Americas, and 56 minutes on EU:
https://i.imgur.com/LPtOrJE.jpg
I was within 10 minutes of the first person to hit 70 on Asia & EU. So, I'm saving Death Breath for when I hit 70, which will help post 70. You have an 86% chance of getting the Grasps of Essence. Even with 4 necros, there's a 30% chance of not being able to get a Bloodtide Blade. Is that difference worth an extra 15 minutes?
Third, the other player can play whatever class they want to, and they don't even need to open up their Challenge Cache for the leveling process.
It's similar to the above start:
Start separate games.
Necromancer:
Gear to buy :
Act 1: Weapon (preferably with +XP) and the 4 armor pieces.
Gear to craft
Level 5 Axe
Level 5 Phylactery
Level 12 Sword
The other player will just search on T6 at level 1 for the following three chests:
Cursed Spire (best)
Cursed Peat
Cursed Bellows (worst)
If they find one, they just wait.
Run Temple of the Firstborn on T2 until level 10+. At level 10+, you'll buy +dmg/int rings/amulet. You'll join their game. They'll exit the game. If they found Spire, they'll just wait at the character screen. If not, they'll exit the party and continue looking for a chest, or looking for a better chest. Grab Kanai's Cube. The Elder Sactum is an amazing spot to get a massacre bonus. You're goal is to be level 22+ by the time you grab it. If you're in a game with Spire, or they haven't found a better Cursed Chest, they can join back in to grab it. This part is typically 15 minutes, which is more than enough time to find one of the three chests.
The other player will hold the game with the Cursed Chest, and you'll exit the game to form a new game and buy the best gear you can. I tend to mainly check the Act 1 & 5 ring vendors (and any close vendors to them), which tend to be the fastest ones to reach. Then you'll join the game. They'll wait at the waypoint, and you clear the Cursed Chest. Have them teleport to you after the timer runs out, and while you're still clearing the remaining enemies to speed things up.
Both players exit the game.
The necromancer starts their own game and goes to buy better gear. The other player searches for one of the following chests:
Cursed Spire
Cursed Peat
Cursed Bellows
Cursed Court
Cursed Cellar (do not do on hardcore)
Cursed Temple
Basically, repeat the first Cursed Chest. They wait at the waypoint, teleport near the end to collect loot, you clear the Cursed Chest, etc.
At this point, you two will play separate games until the necro can use their Level Reduce weapon (make sure it has Life on Hit). If under Level 38, run Cursed Chests on T4. If Level 38 or above, play on T3. They'll go grab the cube if they haven't gotten it yet, or just continue to level up however they want while they wait.
When you can use a Level Reduce Weapon, search for Cursed Chests, but now invite them. They'll wait at the waypoint, and teleport when the timer runs out to speed things up, etc. You'll be playing T6 all the way until Level 66. At Level 67+, you'll set the difficulty down to T5. Between every Cursed Chest, both of you should be looking at vendors for the best gear you can. And when either of you hits Level 61+, craft as much Level 61 gear as you can.
When you're Level 70, now both of you will search for Cursed Chests. They'll search on T6 until Level 67, at which point they'll drop to T5. You'll stick to T5(70). And when they hit Level 61+, have them try to start tagging monsters as well for their own Massacre Bonus. For more expert players, they won't actually wait by the waypoint, rather teleport to the necro, and start tagging as well. Provided they stick by the Necro, they should be able to survive. But like I said earlier, this was with a brand new player, so I'm focusing more on a fast working method to 70, rather than a super efficient working way to 70.
Skills:
Corpse Explosion: Close Quarters
Blood Rush: Potency
Command Golem: Flesh Golem
Bone Armor: Vengeful Armaments
Bone Spikes: Sudden Impact
Land of the Dead: Frozen Lands (if they're also tagging)/Shallow Graves (if they're at waypoint)
Stand Alone
Commander of the Risen Dead
Final Service
Some improvements to be made:
First, if you can get the other player to practice this as a necro too, there's a 98% chance of at least one of you getting Grasps of Essence. This significantly beats Bloodtide Blade, where a group of 4 has a 30% chance of not getting it, at which point, their leveling will take far longer. They're basically a backup incase you fail to get it.
Second, if the other player goes after Leoric's Crown, Ring, or Pox Faulds, the leveling will go faster.
Third, if they can use a survivability build to tag monsters, they'll level faster to 70. If they're a monk or barbarian, you can play T6 all the way to 70. And once you hit 70, you're going to be gaining paragon levels anyway, to help with your stats.