Visceral Ward. The Viscera Devourer gains a +2 bonus to all saving throws and AC while it is grabbing one or more creatures.
Devour Viscera. At the end of the Viscera Devourer draws life energy from every living target it has grabbed. A grabbed target takes 5 necrotic damage per viscera tendril grabbing it, and the Viscera Devourer regains the same amount of hit points.

Multiattack. The Viscera Devourer either makes two Claw attacks, or a Claw and Hungry Viscera attack (if able).
Claw. Melee weapon attack, +10 to hit, one target, Hit: 13 (2d8+4) slashing damage plus 10 (4d4) Necrotic damage, and targets total hit points amount is reduced by an amount equal to the Necrotic damage inflicted until the end of their next long rest, or until they receive the benefits of a Greater Restoration, Heal or Wish spell.
Hungry Viscera. Melee weapon attack, +10 to hit, one target, Hit: 7 (1d4+4), and the target is grabbed (until escape). A Viscera Devourer has four tendrils and can grab up to four creatures, or multiple tendrils can grab a single target (the Viscera Devourer gets  +2 on grappeling checks gainst the target per additional tendril grabbing it).