He/She has a aurorus which well idk what to use i think its ice rock so normal type supa effective also a kangaskan with mega and is a beast i have no idea wth to use with kangaskhan[mega]
aparrently inmunities do 4xtimes normal damage so one thunder bolt from your gardevoir should anihilate garchomp, as for the greninja any strong neutral hit can eliminate its defences
Also this has nothing to relate but i remember that i was a lucky bastard when fighting her ,i did not won, it was a draw(her swords dance breloom destroyed my delta chaizard,but the life ord finnished it.) and the game counted it as a victory and i was able to proceed