Multiattack

The giant makes two Slam attacks. If both attacks hit a Medium or smaller creature, the target is grappled (escape DC 15).

Slam

Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 12 (2d6 + 5) bludgeoning damage.

Squatting Pin

One creature grappled by the flab giant must make a DC 15 Strength saving throw. On a failure, a creature takes 22 (5d6 + 5) bludgeoning damage and is restrained until the grapple ends. On a success, a creature takes half the damage and isn't restrained, but it remains grappled until it escapes. While restrained, a creature takes 8 (1d6 + 5) bludgeoning damage at the start of each of the giant's turns. If the flab giant moves, the target is no longer restrained or grappled.