2019-05-03 : Army is a new creature type. It’s possible to control a nontoken Army (perhaps a creature with the changeling ability) and, through combinations of other cards, it’s possible to control multiple Army tokens. When instructed to amass, you may put +1/+1 counters on any of your Army creatures, and you may choose a different one each time.

2019-05-03 : If you don’t control an Army, the Zombie Army token that you create enters the battlefield as a 0/0 creature. Any abilities that trigger when a creature with a certain power enters the battlefield, such as that of Mentor of the Meek, will see the token enter as a 0/0 creature before it gets +1/+1 counters.

2019-05-03 : Some spells that amass may require targets. If each target chosen is an illegal target as that spell tries to resolve, it doesn’t resolve. You won’t amass.

2019-05-03 : You still amass 1 even if that player has no nonland cards to discard.