Historical Rules · 2 February 2024
Rule 701.44a
Official source text from the 2 February 2024 Rules release
To amass [subtype] N means “If you don’t control an Army creature, create a 0/0 black [subtype] Army creature token. Choose an Army creature you control. Put N +1/+1 counters on that creature. If it isn’t a [subtype], it becomes a [subtype] in addition to its other types.”