Gather The Right Crew To Beat Rendain
Advanced mode can be a bit of a challenge. Constantly monitor your position in relation to Rendain during the first part of the fight. His melee attacks have serious knockback potential and if you don't have a dash to get back, that's instant loss of life. Make sure if you get knocked back, it'll be onto another platform. You're going to want to bring good enemy-killing heroes. ISIC, Oscar Mike, Galilea are all strong characters for this fight because, in general, they're just really good damage-dealers.
The in-between boss battles are easier versions of past boss fights so they shouldn't give you too much trouble—they just take a while. The best thing I suggest is trying to burst him down when he returns after the Boss Gauntlet. The snowy platform has a ramp that leads up that you can kind of use to funnel enemies into. During this phase, watch out for the whirling blades he throws because it'll knock you up and turn off ISIC's ultimate. Everyone should be sure to spawn together and move together instead of one by one.