-Mechanical Brain of Cthulu (Motherboard?)
-The Cyber, Contagion, Ria, etc.
-Hardmode boss enemies (Emperor Slime and something for the Queen Bee)
-Prehistoric minibosses post-Golem
-Wall of Shadow for Corruption worlds
-Spirit of Night boss fight if you've completely cleansed your world of the Corruption/Crimson/Hallow/Cyber (Stage II reveals it to be the essence of Cthulhu, no hate plz
)
-Pets for every boss (Green slime for King Slime, small Demon Eye for EoC, small floating brain from BoC, bouncing slime-like flesh from WoF, Demon Eye sized Twins from The Twins, mechanical Baby Eater from The Destroyer, small mechanical Skeletron head from Skeletron Prime, miniature Golem from the Golem, baby shark from Duke Fishron, Christmas Tree sapling from the Everscream, and finally a robotic elf from Santa-NK1)