Sableye is pretty obvious as one of the only priority Sunny Day users (whimsicott really shouldnt use it). Abuser wise, darm and chandy stand out as the best wallbreakers. victreebel as well. It has access to Weatherball (150bp fire move), Power Whip, Sludge Bomb and Sleep Powder. Max speed gives it 524 which is just past scarf ape, but itd be easier to run chandy instead.Nah, tangrowth is terrible on sun offense. Even with a chlorophyll boost its still really damn slow. I'd go with stuff like chandelure, darmanitan, entei, etc. maybe a prankster weather setter like sableye (I've used it before, not even half bad)
Another asunny day setter could be Mega Doom in theory..