"as soon as the troll recovers knock him down again, it depends on the dice but I can't think of anything else right now"<br/>That would be a ready action, and it would be reliant on a trigger "when the troll comes back to life", and it is an immediate reaction.<br/><br/>Generally speaking, your action will proc<strong>after</strong>the troll does something, be it stand up, or attack. I can assure you though that it will probably stand up the after the next time it goes down, unless it learns that doing so is a bad / risky idea. Assuming you manage to down it, that should minimally buy you guys an extra turn, but two party members standing there to drop it is not going to do much good unless it stays down / dead.<br/><br/>And after the first time you guys pull it off (or try to but fail) it will probably attack immediately from prone the next time it recovers.