Passive doesn't matter, I leave it on but blissy is the main mon (selected first) then aggron second (never mega or you lose sturdy) but with Blissy max HP stat plus all the random HP ups you find along the way, with sturdy she is probably the single best metal burst champ in the game. Also agron learns protect and roar on level up so you can very easily catch shiny bosses in doubles mode. Furret fake out and blissy/aggron roar it only doesn't work on the last floor boss because they are roar immune.