I did a Battle Institute test with Revolver, Scutigera, Shuko and Cassandra.
Got up to the last one, who thought it was A-OK to use FOUR trio legendaries (Moltres, Virizion, Registeel and I didn't see the fourth) and lost pretty easily. The KO I got was Shuko using Stone Edge on the Moltres, critical and super-super effective for a massive damage multiple of x6 (rock hits both flying and fire for double damage and crits are a further x1.5.)
The Registeel kept up with support moves, then Virizion (being Grass/Fighting type with the ability Justified, which buffs attack every time a Dark attack hits it (basically Cassandra's only two attacks) Stone Edge'd Shuko, who got critted and fainted. Out comes Scutigera.
Registeel uses Iron Defense. D:
Virizion uses Stone Edge. Super effective and critical on Scutigera.
Sent out Revolver.
Because Revolver's fat and slow, Virizion one shots it with Leaf Blade.
Cassandra is the last one left. With a combination of Sucker Punch, Detect and Snatch, Cassandra managed to edge both Registeel and Virizion's health very low before Virizion managed a lucky hit with Sacred Sword.
Gah.
Revolver - Samurott (water, moves: surf, dive, hydro cannon, razor shell)
Scutigera - Scolipede (bug poison, moves: steamroller, protect, baton pass and poison tail)
Cassandra - Absol (dark, moves: Detect, sucker punch, snatch and night slash)
Shuko - Sawk (fighting, moves: stone edge, close combat, brick break and counter)