It was. Brain screamed "switch!!!" on the obvious priority, I don't. The first thing you KOed would have helped out later on in the match. I know how this game works so yeah, nothing to do but kick myself for stupid mistakes! :3
Basculin is quite mighty in the rain. Adaptability comes into play here as well.
Aqua Tail [90BP] + Adaptability [x2] + Rain Dance [x2] = 360BP combined with Max Attack and a Choice Band can just plainly devastate teams.