Animated Lava

Magma Form. The animated lava can move through a space as narrow as 1 inch wide without squeezing. A creature that touches the animated lava or hits it with a melee attack while within 5 feet of it takes 5 (1d10) fire damage. 

Illumination. The elemental sheds bright light in a 20-foot radius and dim light in an additional 20 feet.

Water Susceptibility. For every 5 feet the elemental moves in water, or for every gallon of water splashed on it, it takes 1 cold damage.

Fire Obsorption. When the animated lava would take fire damage it instead gains that much hitpoints.

Lifeforce Form. The animated lava's size and strength depends on the amount of hitpoints it has, following the list below.

• 1--20 Hitpoints: Tiny, Strength 6
• 21-50 Hitpoints: Small, Strength 10
• 51-150 Hitpoints: Medium, Strength 14
• 151-240 Hitpoints: Large, Strength 18
• 241-350 Hitpoints: Huge, Strength 22

Lava Capacity. The magic that holds the animated lava together can only hold so much. If it's hitpoints ever excede 350 it explodes, killing the animated lava and throwing lava all around it. When it does, every creature within 20ft of it must make a dexterity saving throw. A creature takes 10d8 fire damage and 6d6 bludgeoning damage on a failed save and half that on a succesfull save. 

Multiattack. The animated lava makes two smash attacks.

Smash. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 10 (1d10 + 4) bludgeoning damage and 10 (1d8+5) fire damage. The animated lava has advantage on this attack if it is grappling the target.

 Grab. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 10 (1d10 + 4) bludgeoning damage and 10 (1d8+5) fire damage. On a hit the target is grappled. While grappled like this it is restrained and takes 1d8+5 fire damage a the start of its turn. The animated lava can grapple up to two creatures.

 Lava Throw (Recharge 5-6). Ranged Weapon Attack: +7 to hit, reach 30 ft., one target. Hit: 10 (1d10 + 4) bludgeoning damage and 10 (1d8+5) fire damage. The animated lava loses 20 hit points. 

 Lava Vomit (Recharge 6). The animated lava spews out lava in a 15 ft square. Every creature within that area must make a Dexterity saving throw. A creature takes 10d8 fire damage on a failed save and half that on a succesfull save. The animated lava loses 50 hit points.