March from the Black Gate

Amass usually asked a card to arrive, mutate a token once, and be done: a single instant of counters bolted onto whatever else the spell was doing. This one instead installs a recurring engine on the second turn of the game and never stops paying out. The enters-the-battlefield trigger seeds the Army; from there every attack the Army makes grows it again, so the counter it hands out is the same counter that widens the swing that earns the next counter. That self-reinforcing loop is the whole point, and it is why the effect lives on an enchantment: the permanent has to survive to keep firing, which makes it a target you defend rather than a play you resolve and forget. The Orc typing does real work too, tagging the growing Army as a creature type other cards can reward, so a token that starts at 0/0 becomes both a clock and tribal fodder. What keeps it from running away is the pace: amass Orcs 1 hands out a single counter per trigger, so the Army climbs one step at a time and asks the deck to protect the enchantment and keep attacking rather than to spike in a single turn. It is the go-tall, keep-swinging reading of a mechanic mostly built to make a token big all at once, trading burst for a compounding threat whose engine you have to keep alive.