Am I allowed to choose "protection from everything"? What about "annihilator 6"?

I think there's a limited set of existing ability counters, and the implication is that you'd have to choose from them.

So no "when this deals combat damage to an opponent, they lose the game" counter then? :)

I wondered that. There were the ten punch-out counters in Ikoria. But Ikoria Commander cards had other ability counters including double strike (Avenging Huntbonder) and indestructible (Daring Fiendbonder), so that list isn't exhaustive. I don't know where else you'd draw the line. Modular Monstrosity is allowed to have "protection from everything" and "annihilator 6" (but no higher).

Hi guys, yes I was specifically thinking about the counters from Ikoria. Didn't know there was an indestructible counter, but yeah, that'll work too. If there ever is a 'Progenitus' counter, Alex, the best thing to do is get rid of it as soon as possible. After all, it's the card that has the ability, not the counter itself (I hope).

Surprisingly, this works as intended, other than the correct term being "keyword counter" rather than "ability counter." However, it's pretty ambiguous and people will continue to be confused like Alex was

> 122.1b > A keyword counter on a permanent or on a card in a zone other than the battlefield causes that object to gain that keyword. The keywords that a keyword counter can be are flying, first strike, double strike, deathtouch, haste, hexproof, indestructible, lifelink, menace, reach, trample, and vigilance, as well as any variants of those keywords. See rule 613.1f.

(I think the "variants of" clause just means all the different "hexproof from" abilities)