Post-update:
One of the new Ultra-Rare ( III ) rooms: The Bone Pile, now grants opposing teams Frozen on skull matches for the rest of the delve. Beware.
EDIT: Also beware of the new Rare (II) room, Smuggler’s Den, if you do not have a team that can target individual units. A Bonnie Rose team is going to bring the hurt. This room is harder than it’s rarity class suggests.