I have a custom creature card in my cube. It’s a 0/4 with the text: “Rubblebelt Rioters gets +X/+0, where X is the greatest power among creatures.”
If it’s the only creature in play, it’s a 0/4. If it’s in play with a 1/1, then it’s a 1/4. Easy so far.
What happens if it’s the only creature in play and it has a +1/+1 counter on it? Is it a 1/5? Does it see that the greatest power is 1, so it gives itself +1/+0, then +2/+0, +4/+0 ad infinitum?
I don’t know of any real card with a similar static ability to check the rulings for.
As you say, layers deal with the order that effects are applied but not how many times to apply the same effect. I think the real answer is that the ability doesn’t work when worded this way within the official rules…
Right, thats likely why all of the similar cards i could find on a search were triggered abilities. But, if you go through all of the layers in order then the resulting power after 1 pass will stay that value until something else changes the game-state and causes them to recheck since the +X/+0 will have already been applied.