NOTE: Image credit to @_Alexyssss26 on Twitter (if you by chance see this, and want me to remove it, let me know)
Bosses:
Auto-Chipper: He is a big wooden head encountered in Fazbear Hills and Choppy Woods.
Bouncer/Snowcone- They are a giant snowman with guns for arms encountered in Dusting Fields.
Browboy- He is a giant Balloon Boy like boy with a unibrow, encountered in Pinwheel Circus.
Bubba- He is a giant old destroyed wind-up teddy bear with yellow glowing eyes, encountered in Pinwheel Funhouse.
Chica's Magic Rainbow- She is what her name suggests, a magic rainbow. She is a rainbow with eyes and a mouth who shoots rainbows and is the secret boss of update 2. She also makes a cameo in the movie in the ice-cream shop. She is found in the Geist Lair.
Chipper's Revenge- He is a giant metal version of Chipper who wants revenge on the FNAF gang for taking his place, he is found in the Mysterious Mine.
Eyesore- He is a giant eyeball with roots of the eyeball. He is found in the Mysterious Mine.
Gold Endo- He is a giant golden endoskeleton, encountered in Pinwheel Funhouse.
Mad Endo/Overclock- They are giant endoskeletons with red eyes, encountered in Deep-Metal Mine.
Porkpatch- Confused with Pigpatch by some *cough* Dawko. He is a stuffed Frankenstein monster like pig creature encountered in Deep-Metal Mine.
Purplegiest- He is the fake final boss. He is a pixelated purple monster who resembles Purple Guy. He is found in Geist Lair.
Scott Cawthon- The creator of the games is the final boss battle of the game, or rather, his avatar, Animdude is. Some believe FNAF World was a "vent" game, and Scott's dialogue about how he can't do this anymore and he doesn't want to be the "puppet master" anymore, and showing you how the game ends, sort of hints at that.
Seagoon/Sugargoon- He is a giant kraken type creature. He is found in Lilygear Lake.
Security- He is a giant metal owl with glowing eyes found in Pinwheel Circus.