Which Pokémon did you use once and never again?

Makes sense

If I were to go back and play an older game, I'd know exactly what team I'd be using

I know their PokéDex and what I like from the region

But when it's a new game I leave it to whatever I'm feeling

I'm being totally backward compared to you Z-A is the only game I'm even considering ditching my starter

I've never done that. Maybe if I did competitive play but I've always kept my starter in my team.

One Pokémon that I haven't used yet but I feel falls into that category is Toedscruel. Its ability is very niche or PvP case that permits it to bypass abilities that would otherwise prevent Status conditions from being afflicted but at the cost of having negative priority or going last. Since you're unlikely to ever really come into a situation where you couldn't put an opponent to sleep otherwise, its ability thereby becomes a real hinderance given it has 100 Speed and the point of having Spore in the first place is to put opponents to sleep before they can move. That translates into taking hits that you otherwise wouldn't with another Pokémon(like Amoongus). He does have Earth Power though but doesn't gain it until level 54(forcing you to get it via TM).

I mean its my first pokemon in the game. I have to much loyalty to just box it.