What's a character that's considered useless but you use anyways and for what reason.

Mine is Pyukumuku. It can only learn status moves in sword/shield but I have figured out a way to make it a pain in the ass to get rid of (for single battles in the battle tower). You need pyukumuku to know the moves toxic, recover, and pain split (the last move is your choice), and you need pyukumuku to hold a rocky helment. You use the move toxic first (which poisons the opponent, the poison worsens each turn) then usually go for pain split next (the one with the lower hp will gain some to all of their hp back and the one with more hp loses some hp) then just go for either pain split or recover depending on if you think it can live another hit. The rocky helment hurts the opponent everytime it does a phsyical attack. In some cases you can take your opponent out with the helment or toxic and spamming recover. If pyukumuku faints, which will take a bit since it has decent hp, great defense and special defense, and only has two weaknesses (grass and electric), it is pretty hard to knock it out, but your opponent does, pyukumuku has the ability innards out, which makes the opponent lose the same amount of hp that pyukumuku had before it fainted.