Conjoined Ettin

Four Heads. The siamese ettin has advantage on Wisdom (Perception) checks and on saving throws against being blinded, deafened, stunned, and knocked unconscious.

Wakeful. When two of the siamese ettin's heads are asleep (one on either torso), the other heads are awake.

Multiattack. The siamese ettin makes 4 attacks: one with each arm, given that there is or can be an enemy within reach for that arm.

Battleaxe. (Torso's dominant arm) Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 14 (2d8 + 10) slashing damage.

Morningstar. (Torso's submissive arm) Melee Weapon Attack: +7 to hit, reach 10 ft., multiple targets. Hit: 14 (2d8 + 10) piercing damage. If the attack doesn't stop (because of the ground, building, or enemy, e.g. horizontal sweep that hits no one), the monster takes 5 piercing damage, accounting for resistance.

Stinking Cloud. (Reaction to getting hit by opportunity attack) A cloud of transparent-yellow, nauseating gas centered on the siamese ettin spreads within 5 ft. from the monster in all directions. Cloud lingers only for the duration of the reaction.

Each creature that comes in contact must make a Constitution saving throw (DC14) against poison. On a failed save, the creature spends its action on the next turn retching and reeling. Creatures that don't need to breathe or are immune to poison automatically succeed on the saving throw. A moderate wind (at least 10 miles per hour) disperses the cloud immediately before it can take effect.

Can take four Legendary Actions in total (one round can have multiple) choosing from the list below, and only at the end of another creature's turn, and preferably when the monster is almost dead. 1d6 Legendary Actions are regained after completion of every 15 rounds (ignore maximum).

Demonic Tentacle Grab. Each creature within 20 ft. must make a Strength saving throw (DC20). If there is at least one failed save, amongst the failed saves, the creature rolling the lowest is lifted 15 ft. into the air by a tentacle made of ichor (5 HP) that shoots out of the stomach of the siamese ettin, and the creature grabbed is now Grappled (escape DC 20) and Restrained until the grapple ends or is ended by destroying the tentacle. Target must be Medium or smaller.

Frightful Presence. (Costs 2 Actions) Each creature within 120 ft. of the siamese ettin and aware of it must succeed on a DC 13 Wisdom saving throw or become Frightened 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 siamese ettin's Frightful Presence for the next 24 hours.