Monsters

Day

 * Slimes (Green, Blue, Purple)
 * Pinky
 * Harpy
 * Bunny
 * Goldfish
 * Goblin Scout
 * Bird

Night

 * Zombie
 * Demon Eye
 * Harpy
 * Doctor Bones (rare)
 * The Groom (rare,Blood Moon)
 * Goldfish
 * Bunny
 * Corrupt Goldfish (Blood Moon)
 * Corrupt Bunny (Blood Moon)
 * Werewolf (Full Moon)

After Wall of Flesh is killed

 * Wandering Eye
 * Possessed Armor
 * Werewolf (Full Moon)

Desert

 * Vulture
 * Antlion

===After Wall of Flesh is killed
 * Mummy

Ocean

 * Shark
 * Jellyfish (Pink)
 * Crab

Dirt Layer

 * Slime Monsters (Blue, Red, Yellow, Purple)
 * Pinky (uncommon)
 * Giant Worm
 * Piranha
 * Goldfish (Uncommon)

Stone Layer

 * Slime Monsters (Black, Mother, Baby)
 * Giant Worm
 * Skeleton
 * Tim (rare)
 * Undead Miner
 * Cave Bat
 * Piranha
 * Goldfish (Uncommon)

Corruption Monsters

 * Devourer
 * Eater of Souls
 * Little Eater
 * Big Eater
 * Corrupt Goldfish

After Wall of Flesh is killed

 * Corruptor
 * World feeder (a smaller Eater of Worlds)
 * Slimer
 * Dark Mummy (desert)

Surface Hallow Monsters

 * Pixie
 * Unicorn
 * Light Mummy (desert)

Underground Hallow Monsters

 * Chaos Elemental
 * Illuminant Slime
 * Illuminant Bat
 * Cursed Hammer
 * Enchanted Sword
 * Armored Skeleton
 * Skeleton Archer

Meteor Monsters

 * Meteor Head

Dungeon Monsters

 * Dungeon Guardian
 * Short Bones
 * Angry Bones
 * Big Boned
 * Cursed Skull
 * Dark Caster
 * Dungeon Slime

Immortals

 * Blazing Wheel
 * Spike Ball

Underground Jungle Monsters

 * Hornet
 * Man Eater
 * Piranha
 * Snatcher

Surface Jungle Monsters

 * Snatcher
 * Jungle Bat
 * Slime Monsters (Green, Jungle)
 * Piranha

Underworld Monsters

 * Bone Serpent
 * Fire Imp
 * Demon
 * Hellbat
 * Lava Slime
 * Voodoo Demon

Goblin Army Spawns

 * Goblin Warriors
 * Goblin Sorcerers
 * Goblin Thieves
 * Goblin Peons
 * Goblin Archer

Special

 * Servant of Cthulhu
 * Eye of Cthulhu
 * Dungeon Guardian
 * Skeletron
 * King Slime
 * Eater of Worlds
 * Wall of Flesh
 * Destroyer (a stronger Eater of Worlds)
 * Skeletron Prime (a stronger Skeletron)
 * The Twins (a stronger Eye of Cthulhu)