They can be dual-typed, but at least one of those has to match the type you choose. What type are you choosing, and what’s your team look like?
I would have to choose Bug-type, of course. Team composition would be Galvantula, Yanmega, Heracross, Centiskorch, Genesect, and Rabsca. As to why… I just like 'em, lol. I’m not much of a competitive player. What would your team/type be?
See, I’m the worst about picking Pokémon team comp. I do… Pretty basic coverage in my teams, but I’ve never concerned myself much with squeezing out the most power I can from my team. Not that that’s a bad thing! I’m envious of people who do, lol. But I’m a “fashion over function” kinda guy so most of my 'mons end up getting picked mostly out of design aesthetic… 😅
I have removed overwhelmingly weak options from my teams in favor of stronger Pokémon, but for the most part… It’s like, “oooh, I like that! You’re on my team now,” lol.
Even with my bug team comp, Rabsca only made the cut over Ribombee because I like having a psychic type on my team. I’ve always had a psychic type on my team.