MArcomage

Putrify, Uncommon, 3g
Quick.
Replaces selected Nature card in hand with an Undead card of the same rarity from your deck.

I would remove the "from your deck" element. Otherwise, the player can either use this to summon one specific card (Battalion of fear, most likely) in what is otherwise a Nature deck (easily pulling Rare Natures due to keyword effect), or the player can (intentionally or not) break the effect by not having included an Undead of that rarity in the deck.

Existing card effects that draw a keyword don't limit the results to what's in deck for these reasons. Such summoning cards do one of three things: They pull from all cards of the specified keyword, pull from any card in (either) deck without narrowing the choices, or simply name specific cards that it might draw. (With respect to that last one, this card could be reworked to "Select a rare Nature card from hand to replace with Battalion of fear" and there wouldn't be a problem.)

I think we should just allow it to summon any Undead card of the specific rarity. Summoning Battalion of Fear for just 3 gems is a bit too much.

It will cost the player 8 gems and 2 turns to play a killer card. Especially since rare Nature cards are easily summoned as you pointed out. Keeping it to any rarity though, will have a variety of Undead rares to summon from, ranging from the cheap Battalion of Fear to the expensive Spectral Dragon, so that would keep an average balance in the game and at the same time the way that the rare Undeads would be summoned would be in accordance with the way rare Nature cards are summoned (the pool is 4 Nature rares, where each one serves a different purpose under different conditions and costs)

I agree. As I said at the beginning, just removing the "from your deck" and pulling from the full range of Undead for the targeted rarity would be the best way to adjust this card.