When you fight bosses you are fighting one really good guy instead of 3 bad ones. Now when you fight Bosses that are mainly physical (attacks only or mostly), a simple attack can decimate them. You get a speedy earth type with good mana capacity and teach it barrid or barridis then have it cast the spell for the entire battle sheilding your guys and leaving them open for damage. Though DO NOT use this tactic against a boss like Gojet or another boss that cast sleep, poison, or paralysis moves. Hope it works for you if it doesn't that means you guys are either not strong enough, too low mana or don't have enough speed.