Um, isn't this ": Deal X damage" once you've got at least one counter on something? Which is, uh, a bit good, to put it mildly?

Is the first paragraph supposed to be combat damage? (And indeed, could then be simplified to "Whenever a creature you control deals combat damage")

Oversight on my part, yes that should be combat damage in the first paragraph.

That has the advantage of shortening the text considerably then, since you don't need to mention players planeswalkers etc.

This is still a realllly nice card, mind you. But it takes a bit of setting up; so I see no fundamental problem with it.

Well, it kind of bugs my sensibilities to see a single-card non-bo. Seeing a card that doesn't combo with itself bothers me, like looking at a tile floor which doesn't line up with a tile baseboard. But my sensibilities have been assaulted by far worse things, true, true.

It's still a self combo - it does the setup, it does the explosion once you've set up.

The only likely problem I can see is that all your creatures gaining +1/+1 every turn is likely to win even without that second paragraph.

I mean, the most likely way you'll win with the game with this card is during the post-combat main phase, dumping all the counters you just picked up.