Multiattack

The guardian attacks twice with its slam.

Slam

Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 16 (2d10 + 5) bludgeoning damage. If the target is a creature it makes a DC 15 Constitution saving throw. On a failure its hit point maximum is reduced by an amount equal to the damage dealt. The target dies if its hit point maximum is reduced to 0. A greater restoration spell or similar magic removes the reduction.