Idea for a Suffix, "The Doomsayer"
Would need its own exclusion group, and probably several instances, however basically
a 1/2000 (lower for some bosses) chance an <enemy> will spawn a Boss related too it.
For instance, a 1/2000 any slime can be a Doomsayer, and when killed, spawn a King Slime
Doomsayer Eyes can summon Eye of Cthulhu
Doomsayer Crimson Enemies can summon Brain of Cthulhu
Doomsayer Corruption Enemies can summon Eater,
Doomsayer Sharks in Hardmode can summon Fishron.(1/5000 id say)
Etc,
It adds a new way to farm bosses without the need of crafting their items or wait for them, Plantera would probably need to be killed before Doomsayers for plantera will spawn, same with Moon Lord (1/10000 for moonlord, have doomsayers spawn from the pillars or cultists)
I also feel like Trickster and Petrifying are cruel, day 1 I fought a Trickster Party Animal Green Slime, it destroyed me. (But it was also hillarous to watch it shoot confetti at me) (Another Reason Petrifying is cruel is that there is no counter to it)
Prefix "Pyromaniac"
Causes a firework to go off when attacked or attacking (Once every .5s so rapidfire stuff doesnt crash terraria) because who doesn't like Fireworks!
Prefix "Soul Eater" (Hard Mode)
Excludes Worm Bosses, Whenever a nearby enemy/player is killed this mob Heals to Full
Prefix "Intelligent"
Excludes Flying, Can Open Doors
Prefix "Healer"
Grants nearby hostile mobs a slow Regen, When killed Drops 10 Hearts.
Prefix "Hasty"
Moves 10% Faster
Prefix "Ghostly" (Hardmode)
After Death continues attacking for 3 seconds before dying. (immune to everything for 3 seconds at death/right before)
Prefix "Destructive"
Dealing damage deals 100% More damage, and deals an AOE, capable of killing Players or Enemies.
Prefix "Stealthy"
Has Invisibility, Removed for 10 seconds when dealing damage or taking damage.
Suffix "the Traitorous"
Fights for the Player. (if this is even possible)
Hope you like at least some of my ideas