What's a pokemon that you didn't expect to use but ended up using anyway? (Playthroughs)

I'll give you one; I used a ditto in my first pokemon lets go Eevee playthrough because I was kinda doing a "non-strict" nuzlocke where if a pokemon faints, I can't use it until after the next gym. I thought it would be good defensively. (Because of when it transforms, it would resist the enemy's moves) And it worked to an extent.