Actually, the combo that makes this horribly strong is spine carapace + bone wall
ThisFire Buckler and Thorn carapace are balanced in
duos because you have to give up bone wall, a staple of
decks, to use them.
In your first response you assumed a non-upped bone wall. Upped bonewall costs 5
, not 7
. The quanta cost for this combo is reachable by most rainbows.
Another combo I'd be concerned about is Jade Shield & Diamond Shield. It only requires a duo, and would make you completely immune to spells and most creatures in the game. For just 1
extra you could make the combo unbreakable with PA. All of these combos would still be useful if you only got part of it out as well. Add in a couple SoGs and you have a defense almost equal to RoL/Hope for a lot less cards, and you're immune to spells.
Basically I'm concerned that this card would make any stall deck that wasn't using this card obsolete, because it's a little to easy to set up an unbreakable defense.