Blood Elemental

Blood Form. The elemental can enter a hostile creature's space and stop there. It can move through a space as narrow as 1 inch wide without squeezing.

Multiattack. The elemental uses Leeching Tendril four times and uses Leech twice.

Leech. Melee Weapon Attack: +9 to hit, reach 5 ft., one willing creature, or a creature that is grappled by the elemental, incapacitated, or restrained. Hit: 12 (2d6 + 5) piercing damage plus 7 (2d6) necrotic damage. The target's hit point maximum is reduced by an amount equal to the necrotic damage taken, and the elemental regains hit points equal to that amount. The reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.

Leeching Tendril. Melee Weapon Attack: +9 to hit, reach 5 ft., one creature. Hit: 14 (2d8 + 5) piercing damage. The target is grappled. Until this grapple ends, the target is restrained. The elemental has six Leeching Tendrils, each of which can grapple one target.

Sickening Presence. Each creature that is within 120 feet of the elemental and aware of it must succeed on a DC 16 Constitution saving throw or become poisoned for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the elemental’s Sickening Presence for the next 24 hours.

Blood Rain (Recharge 4-6). The elemental causes blood to rain from above in a 20-foot radius, 40-foot high cylinder centered on a point within 300 feet. Each creature in the cylinder must make a DC16 Dexterity saving throw, taking 22 (5d8) necrotic damage and falling prone on a failed save, or half as much damage and avoiding falling prone on a successful one. The area of the cylinder is considered lightly obscured. The blood rain lasts for 1d3 rounds. If the elemental uses its Blood Rain attack again, the original cylinder dissipates and is replaced with the new one.

Blood Absorption. When the elemental kills a creature with a vascular system it immediately absorbs its blood. The elemental gains 20 temporary hit points, and its size increases to Huge. While Huge, its attacks deal 1 extra damage die of their damage type.