(Hated Tropes) Characters hyped up only to be barely used

The Annihilation Gang (Honkai: Star Rail) - Have a trailer and some promotional images about them but so far never made an in-game appearance besides a few scenes of Duke Inferno (the guy at the center) and very few voicelines from them. Duke Inferno was later killed by Acheron and the rest of the members were vanished from existence.

Vanny (Five Nights at Freddy's) - Was hyped up as FNAF: Security Breach was on its way. When the game released though, Vanny has very little screentime with few chase scenes and appearing in some endings. Vanny and her alter ego Vanessa are quite infamous for having a lot of their content cut.

Adam Warlock (Marvel Cinematic Universe) - Was teased in the Guardians of the Galaxy movies until his debut in the 3rd installment. However, his screentime was lackluster; his only appearances were mostly as haha funny gags. Although he did something in the end, it still felt very disappointing in an otherwise fantastic movie. Hopefully the future Marvel movies do justice to Adam.

Pianosaurus (Poppy Playtime) - Have a trailer dedicated to himself only to have like five seconds of screentime before getting killed... yeah, he definitely have it worst out of all characters here...