Alright, let's fill that reserve slot!
Verxilo you get Deniapede the Venipede. Our poor buggy friend here is in full denial that he is, in fact a bug; therefore, he may not learn any bug type moves, and must solo all bug type Pokemon he sees, trainer and wild. He also shows no fear of Pokemon that are strong against bug, so if he finds himself in battle against a Fire, Flying or Rock type, he will refuse to be switched out.
To evolve, Deniapede must solo Burgh's gym. After seeing how cool his Whirlipede is, he'll be feeling a little better about his true self, so he must learn Steamroller when it becomes available (only after he evolves though).
However, Deniapede runs into a roadblock when your team reaches Skyla's gym. After (probably) spending most of the gym watching his teammates take down bird after bird, he gets really jealous and wants a turn for himself. He must solo Skyla, after which he realizes that hiding his bug typing is only hurting him in the end. From then on, he can evolve into Scoliopede, and must learn every bug-type move available to him when it arrives (X-Scissor via TMs, Megahorn if you have a heart scale). He no longer refuses to switch out upon seeing a Pokemon bug type is weak to, but he still feels the need to solo all bug Pokemon to prove his strength.
That's all, have fun!