@griselbrother it doesn't kill any ravagers or ballistas that already exist, but will kill all future ones played. same effect as Solemnity.
Well, the wording is different, hence my confusion. Solemnity says "can't get counters", whereas this one says "can't have counters". It would make the most sense if all counters are removed, I think.
I'm pretty sure with this play, a ravager still comes in as a 0/0 with a 1/1 counter on it. We'll have to wait for the official ruling but it seems very similar to situations I would run into with Ravnica Allegiance Drafts playing riot cards with simic ascendancy. Since riot creatures enter the battlefield with the 1/1 counter on them, they wouldn't trigger simic ascendancy.