Bloodthorn Mother

Necrotic Absorption. Whenever the Bloodthorn Mother is subjected to necrotic damage, it takes no damage and regains a number of hit points equal to the necrotic damage dealt.

Multiattack. The Bloodthorn Mother makes two slam attacks. If an attack is successful, the target is grappled (escape DC 14). Until this grapple ends, the target is restrained. The Bloodthorn Mother is able to grapple up to two targets at once. 

Slam. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 13 (2d8 + 4) bludgeoning damage. 

Life Drain. Each grappled creature must succeed on a DC 14 Constitution saving throw or its hit point maximum is reduced by 5 (1d6+2). This reduction lasts until the target finishes a Long Rest. The target dies if this effect reduces its hit point maximum to 0.
Using the life essence drained from its victim(s), the Bloodthorn Mother infuses the plants around it with corrupted energy to summon a number of blights.
3-6 HP drained: Summon 1D4 Twig Blights
7-10 HP drained: Summon 1D4 Needle Blights
11-14 HP drained: Summon 1D4 Vine Blights 

Legendary Resistance (1/day). If the Bloodthorn Mother fails a save, it can choose to succeed.