Tactical Defense. Bulo's base AC is 10 + his Dexterity modifier + his Intelligence modifier.

Ooze Cube. Bulo takes up his entire space. Other creatures can enter the space, but a creature that does so is subjected to Bulo's Engulf and has disadvantage on the saving throw.

Creatures inside Bulo can be seen but have total cover.

A creature within 5 feet of Bulo can take an action to pull a creature or object out of Bulo. Doing so requires a successful DC 12 Strength check, and the creature making the attempt takes 10 (3d6) acid damage.

Bulo can hold only one Large creature or up to four Medium or smaller creatures inside it at a time.

Transparent. Even when Bulo is in plain sight, it takes a successful DC 15 Wisdom (Perception) check to spot a cube that has neither moved nor attacked. A creature that tries to enter Bulo's space while unaware of him is surprised by Bulo.

Spellcasting. Bulo is a 5th level spellcaster. He has the following spells prepared.

Cantrips (At will):[Tooltip Not Found], fire bolt, toll the dead

1st level (4 Slots):burning hands, chromatic orb, thunderwave

2nd level (3 Slots): Darkness, dragon's breath

3rd level (2 Slots): Counterspell, fireball

Multiattack. Bulo makes 4 Tendril attacks, 1 Reel attack, and uses Engulf.

Tendril. Melee Weapon Attack: +9 to hit, reach 65 ft., one creature. Hit: 10 (3d6) acid damage, and the target is grappled (escape DC 17). Until the Grapple ends, the target is restrained and has disadvantage on Strength Checks and Strength saving throws, and Bulo can't use the same tendril on another target. 

Engulf. Bulo moves up to his speed. While doing so, he can enter Large or smaller creatures' spaces. Whenever Bulo enters a creature's space, the creature must make a DC 12 Dexterity saving throw.

On a successful save, the creature can choose to be pushed 5 feet back or to the side of Bulo. A creature that chooses not to be pushed suffers the consequences of a failed saving throw.

On a failed save, Bulo enters the creature's space, and the creature takes 10 (3d6) acid damage and is engulfed. The engulfed creature can't breathe, is restrained, and takes 21 (6d6) acid damage at the start of each of the cube's turns. When the cube moves, the engulfed creature moves with him.

An engulfed creature can try to escape by taking an action to make a DC 12 Strength check. On a success, the creature escapes and enters a space of his choice within 5 feet of Bulo.

Reel. Bulo pulls each creature grappled by him up to 50 ft. closer.