Add Goblin. A goblin within 5 feet of the battle stack can use its action to join an existing battle stack. The battle stack's hit points and hit point maximum increase by an amount equal to the goblin's current hit points.

Battle Stack. If the battle stack takes 10 damage or more on a single turn, but not killed outright, one of the goblins dies, and the battle stack must make on a DC 10 Dexterity saving throw at the end of that turn. On a success, the battle stack remains intact (albeit one goblin shorter). On a failed save, the stack collapses and all the goblins fall prone in a 5-foot-square space. At any given time, the battle stack comprises a number of goblins equal to one plus the battle stack's current hit points divided by ten, rounded up. A maximum of nine goblins can form a battle stack.

If the battle stack is reduced to 0 hit points, it collapses and one goblin emerges prone from its remains.

Multiple Goblins. The battle stack has advantage on saving throws against being blinded, charmed, deafened, frightened, stunned, and knocked unconscious.

Nimble Escape. The battle stack can take the Disengage or Hide action as a bonus action on each of its turns.

Remove Goblin. As a bonus action a goblin can remove itself from the battle stack. The battle stack's hit points and hit point maximum are reduced by 10, and a goblin emerges on the ground in an unoccupied space within 5 feet of the battle stack. The goblin acts on the same initiative count as the battle stack. The goblin can't use actions until after its next turn. The battle stack can’t use this action if it has 10 hit points or fewer.

Multiattack. The battle stack makes one spear attack for every two goblins in the battle stack, rounded down.

Spear. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 9 (1d6 + 2) piercing damage.