Sleeper OP

A character in a video game that is simply too strong (overpowered, or OP for short), but not many poeple realize it (yet), hence the "sleeper" part.

This is likely due to the fact that when a new version of a game comes out, it takes a while for people (including some pros) to adjust to the new meta game and rather stick to the same staple set of popular overpowered characters (sometimes despite nerfs) out of comfort instead of trying to discover new ones.

This is NOT related to special snow flakes that somehow made a bad character work against all odds in 1 out of 100 games; Sleeper OP is legit broken, it's just known by the unenlightened masses.

When the Sleeper OP char becomes common knowledge, it loses that status.

Term originated in League of Legends.

Player A: LUL why you pick the Merchant, he's trash.
Player B: Nah man this is 0.24 Merchant, meta sheep just haven't caught on. Merchant Sleeper OP
*PLayer A gets obliterated by Merchant*
Player A: You just got lucky, Merchant sux!