The main hazards of the dungeon is Warps and Damage Walls. The enemies will shoot out the Warps and the Drones will shoot out the Damage Walls. You will need monsters with NDW+NW in other to move around the map effectively. Merry will decrease your team's ATK in Turn 1. The ATK Down will not wear off. The only way to cure it is through Status Recovery or the Jackalope. The Jackalope will appear once you defeat the Homing Absorber. Focus on those two first before dealing damage to Merry.