Inspired by the corruptions of 8.3 (which were a fun idea but terribly implemented). Class abilities now have drawbacks that negatively impact the player character whenever they are cast.
Here are a few examples:
Fire Mage - All fire spells set the caster ablaze for 1/2/3% of max HP per second depending on cast duration and/or damage done.
Frost Mage - All frost spells add a stack of Bone Chilling, slowing the caster by 5%, lasting 10s. At 10 the stacks are consumed and the caster is entombed in ice and rapidly loses HP. Can be broken free by teammates.
Arcane Mage: All arcane spells consume 1.5 more mana than regular. Additionally, upon reaching 10% mana remaining, the caster loses 5% maximum mana, lasting until the end of combat.
Fury Warrior: While Enraged, you deal 100% bonus damage (ignoring armor and resistances) but are hostile to all other players and pets in the group.
Arms Warrior: Rage replaced with Endurance. Begin with 100 endurance. Each ability consumes Endurance points (depending on ability). Below 50 endurance haste and speed reduced by 25%, below 25 Endurance damage additionally reduced by 25%. At 0 Endurance the player is Exhausted and cannot use offensive or mobility abilities.
Protection Warrior: Speed reduced by 25%, haste reduced by 15%, damage reduced by 10%. Cannot move more than 10 yards at any one point in time.
Incentive for playing scuffed classes: 50% increase in seasonal rewards (anima, azerite, rating, honor, conquest, valor, etc.), 150% increase in regular rewards (gold, reputation), 25% increase in item drop, 15% increase in pet and mount drops (current expansion). Special Feat of Strength achievements for clearing mythic and PvP content.
Share your cool ideas for the other classes and specs or even for the two mentioned here.