Non-bueno card. A large number of fire creatures only have 1 hp to begin with. You're insta-killing Lava Golem | Lava Destroyer, Ash Eater | Brimstone Eater, Phoenix | Minor Phoenix, and cutting a chunk out of the rest of their low hp creatures (instakilling Ruby Dragon with upped). Not to mention this makes some of the best rush creatures in the game more powerful instantly. Basically, if this card comes out, Fire will see a substantial drop, while Forest Spectre decks take the metagame by storm.
HOWEVER, Fire Buckler does similar things to fire creatures. This might be balanceable, but I'm still leaning away from this.