See Nightmare Lurker.

Still brainstorming. I don't really like this; it's too close to trample.

Oh, it's an interesting thought, though. In some ways it's similar to trample, in that it can get damage through, despite being in UB. But in another way it's quite a drawback, because you can't trade, so if opponent can block you at all, even with a triple-block, they probably come off well.

(Is this supposed to only function on attack? I don't know if it's better or worse if it happened when blocking too...)

It is. I wasn't thinking about that when I created it.

I should add to my list of criteria that the mechanic shouldn't have downsides. Pierce, as worded here, prevents combat damage triggers from happening, and doesn't allow the creature to harm players or planeswalkers.

Oh, I hadn't noticed all of that. Is there a reason not to make it combat damage? "If ~ is attacking a player or planeswalker, it deals combat damage to that player or planeswalker, not to blocking creatures" or something?

That's possible, but then it really becomes super trample.

This is already just a weaker super trample.

Yes it is.

Or, come to think of it, you could keyword the "when this attacks, defending player loses 2 life" ability, and use it on 0-power creatures. I don't know if that would feel similar/different.