So I set myself a challenge on USUM, to beat the Battle Tree using only bug types. I did it after much experimentation.
Singles was pretty easy, just set up hazards with Crustle, exploit Truant Durant to entrain, then bring in Scolipede, set up swords dances and sweep through with Aqua Tail and X-Scissor, with Waterium Z. Water has best type coverage for Bug.
Doubles was significantly harder. I finally won with a squad of:
Illumise, Araquanid
M-Scizor, Volcarona
Araquanid and Illumise lead.
Araquanid, Max attack, Max HP, Adamant
Leftovers
Stockpile, Wide guard, Liquidation, Leech life.
Illumise, Max HP, 2/5ths of rest into Def, 3/5ths into SpD, Calm
Normalium Z
Prankster
Charm, Struggle Bug, Encore, Psych Up
The basic strategy is that Araquanid starts stockpiling while Illumise weakens their attacks. Once Illumise is down to low HP, it can use Z-Psych Up, which restores all of its HP, and grabs Araquanid's defense boosts. If a fire or rock type comes out, I prefer to go for immediate Liquidation. If I sense a rock slide is coming, I use Wide Guard and Charm it. Encore for maximum carnage and allowing Araquanid to boost up. Much like the Durant strat, this abuses the AI's unwillingness to switch out. Once one of the two leads go down, Volcarona and Scizor can come in, boost up and take everything out.
Volcarona, Max HP, Max Def, Bold, this will allow to be touched by a rock
Aguav Berry
Heat Wave, Giga Drain, Roost, Quiver Dance
M-Scizor, forgot his IVs
Bullet Punch, Bug Bite, Swords Dance, Protect
For other good bugs I used while experimenting, there's:
Accelgor, best of the rest for doubles
Ribombee, built for doubles but its utility is more useful against human opponents
Buzzwole, no good utlity and inferior to M-Scizor
M-Heracross proved inferior to Scizor due to speed
Pheramosa, a better M-Beedrill with some utility
Vivillon was good partnered with Scizor for Powder and Sleep Powder support
Shuckle, good for Guard Split shenanigans
