Dreadhorde Invasion

If you don't control an Army, the Zombie Army token you create enters the battlefield as a 0/0 creature before receiving counters. 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.

To amass Zombies N, if you don't control an Army creature, create a 0/0 black Zombie Army creature token. Then you choose an Army creature you control and put N +1/+1 counters on it. If that Army isn't already a Zombie, it becomes a Zombie in addition to its other types.

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.

Some cards that cause you to amass Zombies also provide bonuses to "Zombie tokens." These affect any token that happens to be a Zombie, not just a Zombie Army you've amassed.

If the token's power changes later in the turn after it has attacked, including while Dreadhorde Invasion's second ability is on the stack, it won't cause the token to gain or lose lifelink.

The power of the Zombie token is checked only immediately after it attacks. Any other abilities that trigger when creatures you control attack won't have resolved yet.