Mismagius is a pure Ghost type and evolved form of Misdreavus, as well Mismagius has an absolutely amazing design and suits it well. Mismagius is also decent in playthroughs as it has alright stats/movepool/abilities (I don't think I've ever used it, but definitely viable) Anyways, as much as I love Mismagius, this just seemed to be the best fit to start out my top 20 which is why I chose to rank this here.
2nd - Mamoswine
3rd - Electivire