Any of the death-rattle affixes.
Sanguine
Bolstering
Bursting
Spiteful
Quaking when playing a caster.
In general I think the affixes and what they are to M+ need to be reworked. Here is my take… and it is probably a bad one.
They keys will naturally get more difficult with multiplicative scaling. There will always be a cap that everyone will hit.
So let us go nuts with it. Have affixes that have no negative impact for not doing them. But, give them a positive impact for doing them well.
Afflicted? Have their health bar tick down from the debuffs. When the die nothing happens. When it is cleansed off? They explode dealing their remaining health in damage to nearby enemies.
Bursting? Killing mobs grants a 20 second haste buff. The more mobs you kill the more stacks you get. The stacks do not affect the duration of the buff. So it encourages get a bunch of mobs low. Then Blast them all down quickly and run to the next pack with the haste buff.
Volcanic? A volcano spawns. Standing in it when it enterrupts causes your spells and abilities to deal extra fire damage for the next 8 seconds. Or their healing spells to give the player a molten barrier, absorbing 15% of the damage healed lasting 8 seconds.
Quaking: You get a debuff. If you stand on enemies when the debuff is dispelled or drops off, you drop an earthquake. The earthquake slows melee attack speed and spellcasting speed by 20% for 5 seconds.
Incorporeal: CC’ing the Incorp before it despawns, causes the incorporeal to cast healing spells on group members who are below 70% health, or deal damage to nearby enemies for 10 seconds.
Bolstering: Killing an enemy causes it to yell a death rattle. Nearby enemies take 4% more damage for 10 seconds. This effect stacks. Adding stacks does not refresh the duration. Bosses cannot be bolstered.
Sanguine: Random enemies in the dungeon have the sanguine affix. When and enemy with the sanguine affix dies they drop a sanguine pool. The pool lasts for 8 seconds. Players standing in sanguine have their leech increased to 30%.
Spiteful: When enemies die they spawn a Spite for a random player. This spite only appears to that player. The spiteful add runs away from the player. If the player catches the spiteful add, their damaging abilities have a chance to deal additional shadow damage to enemies, and their heals cause the target to take 20% less damage for 4 seconds.
These are just some off the cuff ideas. Have them all be fun. Then just let the key scaling work itself out on the limit keys can be pushed. Hell increase the scaling a bit with the positive affixes.
I am not saying its a perfect solution. But, I guarantee more people would run keys and have a better time doing it. And think of all the degen things MDI and TGP players can create using positive affixes.