"Once per turn" triggers
Board state: I have on board [[Blech, Loafing Pest]], two Pests, and [[Hollowmurk Siege]] (having chosen Sultai).
Initiating event: I gain 1 life, triggering Blech to put a counter on himself and each of the two Pests.
Question: how many cards do I draw from Hollowmurk Siege?