[Coda]

The best way to deal with that dungeon at low level is to stack HP and RCV with dual-element monsters. You're going to need a MINIMUM of 14,000 HP to clear the dungeon if you don't have enough dual-element monsters (and skill at making combos) to wear through the masks 1HP at a time before they hit you. If you ARE good enough at the combos, then you can theoretically clear the dungeon without taking more than one hit of 4000 damage -- nothing has more than 18 HP, and a full team of dual-element monsters can deal 12 damage per round, and only the Mystic Mask has a short enough cooldown to hit you before you can take it out that way. (And if you bring poison, you can take it out before it swings.)

At higher levels, stacking ATK and Two-Pronged Attack can pierce through the defense of the masks.

That said, my Wednesday Dungeon team is a Physical dual-element team with over 75k HP, because it's the more reliable option.

Zombie teams (Odin or ogres) don't work terribly well because you'll die if you ever come across a round with two monsters on the same countdown.