Multiattack

The sentinel attacks three times.

Halberd

Melee Weapon Attack: +5 to hit, reach 10 ft., one target. Hit: 8 (1d10 + 3) slashing damage.

Calculated Sweep

The sentinel makes a melee attack against each creature of its choice within 10 feet. On a critical hit the target makes a DC 13 Strength saving throw falling prone on a failure.