Some cards refer to the "amassed Army." That means the Army creature you chose to receive counters, even if no counters were placed on it for some reason.
Swarming of Moria
Amass Zombies works the same way, except you create a 0/0 black Zombie Army creature token if you don't control an Army. If the Army creature you chose isn't already a Zombie, it becomes a Zombie in addition to its other types. By combining cards with amass Orcs and amass Zombies, you can end up with an Orc Zombie Army.
Amass abilities are now written as "amass [subtype] N." Previous cards with amass have received errata to say "amass Zombies N."
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Pavel Kolomeyets
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
