Yes, poison counters are cumulative , which is the only way you'd usually be able to win with poison
All you have to do is tap Carnival Barker and get as many people to applaud your creature as you can in a 30-second timeframe
Now, as I always say, a card like this might lose its edge if we get more late-game options to get our resources back, but for the time being, I think some decks will be very happy with Tarragon
It's an aura that gives creatures different stats and a few various keywords
But the legendary has since risen in value as Soldiers remains a popular Standard best-of-one meta deck
Meaning that if you have a way to discard it in the first place, creatures, enchantments, and sorceries with madness can be cast at instant speed