The Rats is a collective slang term that refers to the following characters:
"The Rat" originated as a disparaging nickname for Pikachu in Super Smash Bros. due to its long-standing status as that game's undisputed best character. "The Rats" was then later adopted by Ultimate players as a term to refer to both Pikachu and Pichu collectively, as is frequently applicable due to being clones of each other, and often with similar negative connotations. The term could also apply to Pikachu and Pichu in Melee where they are even closer clones, but due to Pichu being practically competitively irrelevant in Melee, the term never saw widespread usage among its playerbase.