Innate Spellcasting. The juggernaut's spellcasting ability is Wisdom (spell save DC 15). The juggernaut can innately cast the following spells, requiring no material components:

1/day each: dominate person, feeblemind

2/day each: disintegrate, invisibility (self only)

Reckless. At the start of its turn, the juggernaut can gain advantage on all melee weapon attack rolls it makes during that turn, but attack rolls against it have advantage until the start of its next turn.

Running Leap. The juggernaut’s long jump is up to 40 feet and its high jump is up to 20 feet when it has a running start.

Multiattack. The juggernaut makes three attacks: two with its fists and one with its tentacles. 

Fist. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 22 (3d10 + 9) bludgeoning damage.

Tentacles. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 19 (2d10 + 9) bludgeoning and 13 (2d4+9) piercing damage. 

Charge. If the juggernaut moves at least 20 feet straight toward a target and then hits it with a fist attack on the same turn, the target takes an extra 9 (2d8) bludgeoning damage. If the target is a creature, it must succeed on a DC 18 Strength saving throw or be knocked prone.

Ichor Spray: As a reaction, the juggernaut can release a spray of ichor, covering all hostile creatures within a 15 ft radius. Affected creatures must succeed on a DC 18 dexterity saving throw or take 8 (2d6) poison damage and be frightened of the juggernaut until the end of their next turn. Creatures frightened by the juggernaut cannot voluntarily move closer to it and have disadvantage on all attacks while it is in their sight.