Fascinating! Works its way towards being the harsh side of Jin-Gitaxias, but gradually.

It's a pity you have to keep adding the counters even after its power is very negative.

At least functionally, negative power behaves the same as 0 (there might be a few weird exceptions?) I feel like if you're building a deck around this, you'd have some appropriate support (like flickering... note to self, maybe flickering is something I can explore in this block).

I think what Alex is getting at is that it's annoying to keep adding counters to a creature long after the point where it's not important. Some people will just stop adding counters, and stop caring, and some people will keep adding counters and enjoy their foolishness. But some will keep adding counters and be annoyed that the game is 'forcing' them to do it. It's not a reason to not print a card, but it's worth noting.

In theory, I'd be concerned about the Lumbering Satyr effect. I used to have a bet Black/Green deck that wasn't really Black-Green. It just packed 4x Lumbering Satyr, 4x Hickory Woodlots and 2x Havenwood Battlegrounds. 5/4 for 4 with no drawback, which gave all my creatures Forestwalk? Yes, please!

Or, in other words, you could always drop Guomm on the battlefield with Resurrection and never lose an ounce of power. That said, you can't attack with him, without pulling another card into this combo, so nice touch there.

Yes, this isn't too worrying from that point of view: you can use it as a 12/6 wall in a deck with no black mana, using something like Master Transmuter, but it's still just a wall. (You can get one attack with it, using Yore-Tiller Nephilim or Through the Breach, but again, there are better things to do with that if that's all you're going for.) You can also use it for things like Fling or Fall of the Hammer in tasty fashion. And of course there's always Warmonger's Chariot, which makes this very scary, but then there's the black mana problem to work around.

What I'm saying is that this is great because there are lots of good ways to use the card, but none of them are broken.

Jmg is right about what I meant with my earlier comment. Theoretically the game requires you to keep adding counters even after this has 12, or 16, or 20. And it could theoretically matter because someone might have a Howl from Beyond or some such. But in practice it never will.

It's damn nice with anything that throws power at people, or wall animators or... too.

And I kinda like the idea of gifting it, so that you can have a nice huge hand size, too. Combine with all those creatures who have power equal to cards in hand, and go to town.

That would be the Fling and Warmonger's Chariot that I mentioned, yes?

But hee, I hadn't even thought of donating it :)

Interesting points, all. My other of these 'mana eaters' have some sort of counter dump mechanic, so perhaps I can add "If Guomm's power is ever negative, remove all counters at the beginning of your end step."

That'd address the gripes with having to keep adding counters into the negative, as well as making it a bit more dynamic in play... I'll think about that.