Couldn't it be something like,

Banling
As an additional cost to cast Baneling sacrifice a zerg creature.
If Baneling would deal combat damage to a creature or player, sacrifice it at end of combat.
3/1

patrik123: The "sacrifice another creature" is certainly flavorful, though the low casting cost and inflexibility of the design would make it a poor late-game creature. And as mentioned in one of the comments here, card flexibility is very important when working with design space as tight as a duel deck. :)

comparing to the rest of the set, unless this is specifically designed to be underwhelming, I'd just cost one of the two mana costs at just . In practice you're activating this to trade it, with vanishingly small upside of cashing it in as the world's tiniest lava axe. That's not worth it for a 2 mana 1/1.

Don't underestimate the power of flash gray Ogre, even if it dies EOT.

Also remember that "threat of activation" is a powerful thing.

rswitzerloot: What Doombringer said. Just the threat of activation and open mana can allow this to be a good blocker, and the threat of an EOT Baneling will make anyone think twice about attacking all-in without keeping even an SCV to block. Also, sometimes the world's tiniest Lava Axe can be snuck through a (((Nydus Network))) and seal the win. :)

The more interesting question I've always faced with this card was whether to cost the ability at or . Tiny lava axe is good, but pumping 10+mana into surprise Blaze feels like a cheap win.

Looks like Perilous Myr to me. Reasonable - the myr is on the strongish side. Also, as we know, color pie is a thing so at least in black it can be argued for instead of generic mana / any color. Especially with the Skeleton Archer direction WotC seems to be heading.