Terraria has 66 different enemies to fight.
Common enemies
Angry Bones Antlion Bat
Bird Blazing Wheel Bone Serpent
Bunny Corrupt Bunny Corrupt Goldfish
Crab Cursed Skull Dark Caster
Demon Demon Eye Devourer
Dungeon Guardian Eater of Souls Fire Imp
Giant Worm Goblin Scout Goldfish
Harpy Hornet Jellyfish
Leech Man Eater Meteor Head
Piranha Servant of Cthulhu Shark
Skeleton Slime Snatcher
Spike Ball Undead Miner Voodoo Demon
Vulture Zombie
Hardmode enemies
Angler Fish Armored Skeleton Chaos Elemental
Clinger Clown Corrupt Slime
Corruptor Cursed Hammer Dark Mummy
Digger Enchanted Sword Gastropod
Giant Bat Green Jellyfish Illuminant Bat
Illuminant Slime Light Mummy Mimic
Mummy Pixie Possessed Armor
Probe Skeleton Archer Slimer
Toxic Sludge Unicorn Wandering Eye
Werewolf World Feeder Wraith
Wyvern
Rare enemies
Doctor Bones Nymph The Groom
Tim Pinky Rune Wizard
Angry Bones Antlion Bat
Bird Blazing Wheel Bone Serpent
Bunny Corrupt Bunny Corrupt Goldfish
Crab Cursed Skull Dark Caster
Demon Demon Eye Devourer
Dungeon Guardian Eater of Souls Fire Imp
Giant Worm Goblin Scout Goldfish
Harpy Hornet Jellyfish
Leech Man Eater Meteor Head
Piranha Servant of Cthulhu Shark
Skeleton Slime Snatcher
Spike Ball Undead Miner Voodoo Demon
Vulture Zombie
Hardmode enemies
Angler Fish Armored Skeleton Chaos Elemental
Clinger Clown Corrupt Slime
Corruptor Cursed Hammer Dark Mummy
Digger Enchanted Sword Gastropod
Giant Bat Green Jellyfish Illuminant Bat
Illuminant Slime Light Mummy Mimic
Mummy Pixie Possessed Armor
Probe Skeleton Archer Slimer
Toxic Sludge Unicorn Wandering Eye
Werewolf World Feeder Wraith
Wyvern
Rare enemies
Doctor Bones Nymph The Groom
Tim Pinky Rune Wizard