I don't like this. It is too much of a Sengir Vampire type ability, where it is powerful enough that your opponent will play around it but will never have to trigger it, so it won't live up to the promise. I would rather pay mana and tap or trigger when it hits a player and that is assuming we want to be stealing counters. Also consider making it like Bloodcrazed Hoplite where you get half of the value even if there is nothing to steal.

Good Point. Do we have end step raid triggers? If so, it could just be Raid Bloodcrazed Hoplite

It can block countery creatures. If we make it 3/2, it's more of a choice whether to block it with them or let it through. alt: Raid—When ~ ETB, if you attacked with a creature this turn, put a +1/+1 counter on ~ and remove one from a creature an opponent controls.

If you do it as a 1 time etb we may want to push it up the scale a bit so it doesn't come down before your opponent has put counters on their creatures. (Not that black raid creature wants to be too big)

true. then it loses flavor. fair to scrap this.

I was wondering about repeating raid triggers, like they did for morbid in conspiracy

We made Honor of the Vanara and Channeler of the Untamed being repeatable. I think the problem is that the GW archetype relies on +1/+1 counters. I am afraid of making this card too good in that one matchup. I would rather have a strong body and a weak ability that is extra good against a specific archetype, than a weak body and a strong ability that is extra good against a specific archetype.