(if it does not fit, just sleepy) the Munna.
This Munna is so tired, it must always know and use yawn as its first move in battle. Following that, ASAP, its only attacking moves that it can use is future sight, which will be replaced by dream eater, and nightmare. The last move may be any supporting move, such as moonlight, calm mind or whatever. It may evolve into Musharna after soloing the entire ground gym, including the gym leader. Finally, it has to solo Caithlin, the psychic-elite four member.
It somehow hates all psychic types, so it wants to solo them all.
GL (know that I have been very mild towards you, I could have changed that to dark types and the dark type elite four