To glitch, the verb, is a common slang term in the Pokémon glitch community that simply means to change something in a game to what it should not normally be. This usually happens after a glitch is done, creating the term. Conjugation for to glitch is that of all regular English verbs.
As an adjective
The form "glitched" or "glitchy" may also be an adjective describing the state of a game after a glitching, or of a specific Pokémon or item affected by said glitching. A common example is a "glitched Hall of Fame" in Red/Blue versions, created after an encounter with MissingNo., or a "glitched Kangaskhan" created through evolving the glitch Pokémon 'M.