From SmashWiki, the Super Smash Bros. wiki
The Sheriff universe (シェリフ, Sheriff) is a universe that is represented in Super Smash Bros. 4 by the Sheriff assist trophy. The franchise consists of two games, Sheriff and a simplified remake named Sheriff 2, both developed by Nintendo for arcades in 1979.
The titular Sheriff appears as a trophy.
Sheriff is the only universe in the series to be represented in one installment, get completely dropped in the next installment, and then make a comeback in the very next installment.