This ability feels natural; but is kinda hard to word to make it work right. But that's not the real problem. People would usually chump this anyway. The real problem is that this is a very cheap defensive creature as well.

"Must attack each combat each turn if able, and must be blocked if able." Although now it's starting to feel like a red The Abyss

@Vitenka: I don't think 'it makes a good defender' is a problem for the mechanic per se. It just means we need to be careful how the creature gets costed.

­Grave Bramble isn't the best card to bring forward to figure out if this card is undercosted, since it's a common from a 7 year old set. But it does help establish a baseline. Brambles has a bonus against zombies. But Sightless Stomper can take a swing at any untapped creature. That's a huge upside. There's an argument to be made that that ability is better than the ability to attack opponents.

4/4 for is the highest I'd go for rare. It's possible that even that's too good, but I'd want to see it in action before I made that call.

I was personally thinking of Glade Watcher in terms of costing, making it a bit more efficient due to being a rare... though in retrospect I overshot in that regard. A 4/4 for that cost does seem fair, but it also feels a bit less splashy. Maybe a a 6/5 or 5/6 for 4? It would still be over-statted for its cost, but not by the same degree, and 3 to 4 is a significant jump in mana cost.

Or maybe not, I can never quite get the hang of the dials and knobs.