Almudron

Mire's Grasp. The Almudron can move through rough terrain created by swamps or bogs with no penalty. 

Slipstream. The Almudron dives down, traversing under muddy water to a different location up to its burrowing speed.

Multiattack. The Almudron makes three attacks

Lunge. Melee Weapon Attack: +8 to hit, reach 10 ft., 1 target. Hit: 19 (2d10 + 7) [damage type] damage. 

Mud Sling. Ranged Weapon Attack: +8 to hit, range 20/60 ft., 1 target. Hit: 15 (2d6 + 7) bludgeoning damage. The creature hit by this attack must make a DC 17 dexterity saving throw or be slowed until the start of their next round.

Coiling Earth. Melee Weapon Attack. +8 to hit, reach 10 feet. 1 target. Hit 17 (2d8+7) bludgeoning damage

The Almudron can take up to 3 legendary actions during the round, at the end of each of the player character's turns

Sludge Wave (Costs 1 Action). The almudron winds up an attack that looks like the coiling, except it does not hit a target and instead sends out a wave of mud and grime up to 60 feet, stopping if it hits an object. A creature caught by the wave must make a DC 17 dexterity save, taking 3d6 bludgeoning damage, halved on a successful save. On a fail, the creature has its movement reduced by 10 feet a round.

Keening Call (Costs 1 action). Every creature within 30 feet of the Almudron must make a DC 17 wisdom save or be charmed by it until the start of its next turn.

Clay Mace (costs 1 action). The Almudron forms a large ball of clay and mud on the end of its tail, and makes a melee attack against a creature within 20 feet. +8 to hit, 1 target.  24 (2d12+8) bludgeoning damage