Batiri Battle Stack

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 falls prone or takes 10 damage or more on a single turn, it must make on a DC 10 Dexterity saving throw at the end of that turn. On a failed save, the stack collapses and 2d4 goblins emerge prone in the space occupied by the battle stack.

If damage reduces the battle stack to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken. On a success, 1d4 goblins emerge prone in the space occupied by the battle stack, each with half their hit point maximum.

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

Multiattack. The battle stack makes two Spears attacks.

Spears. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit:  7 (2d6) piercing damage, or 3 (1d6) piercing damage if the battle stack has half of its hit points or fewer.

Eject Goblin. The battle stack can eject a goblin, which appears in an unoccupied space within 5 feet of it. The battle stack's hit points and hit point maximum are reduced by 10. The ejected goblin acts on its own initiative count.