I was thinking about c!Grian having a Pokémon team and why he would have certain Pokémon, so here are my thoughts!
Talonflame! He got Talonflame as a Fletchling, which was his starter. I'm not sure where he would obtain Fletchling, but I imagine it doesn't have a Pokéball. It just hangs out. Grian uses it to send messages to other hermits when he doesn't have his comm on him!
Chatot. I just think a Chatot would suit him, being a parrot and all that. Chatot would help him pull pranks by mimicking sounds like creeper hisses, pistons, etc... I imagine this is a fairly new addition to the team, a gift from X to him in HC6 as a housewarming type of thing.
Beheeym. Honestly, just for vibes, with the space things he's got going on in HC11, and the moon thing in HC8, he's got a lot of space going on. So alien pokemon go! Maybe he found it in the Void after HC8.
Shiinotic! Mushrooms :3 Mother Spore :3 that's it. that's the reason. I think he would find it in HC7 during the whole Mycelium Revolution and decide "yeah, that guy's our mascot now" and Shiinotic has been on his team ever since!
Stonjourner. I think it's neat! And it could help with building, being made of rocks, and thus really strong. I think he'd like it. Maybe he found it during HC9 with the Entity.
A Xatu, which he raised from Natu. I imagine in this world, Watchers would give their converts a Natu as a sort of starter Pokemon. He kept it after he left and has a LOt of complicated feelings towards it. It's not Xatu's fault what happened, but there's a lot of trauma associated with that time in his life. He doesn't bring it out a lot.
Maybe I'll do this for other mcyts?? This was fun.