Big Boy (Robot)

Self Destruct. When Big Boy's HP is below 20, roll 1d20. On 11-20, it will initiate Self Destruct that affect 20ft radius.
Any creature that caught in the blast has to roll DC17 Constitution Saving Throw or take 12d8 Fire Damage and blasted away 20 feet from initial position.
On success save,  they take half damage.

MultiAttack. Big Boy makes 4 Attacks in one turn with its free hands.

Fist Barrage. Melee Weapon Attack: +8 to hit, reach 5 ft., 1 target. Hit: 16 (6d6 + 3) bludgeoning damage. 

Slam and Grab. Big Boy slams the target to the ground and grab them. Maximum of 4 creature can be grabbed this way. The target must make DC17 Dexterity Saving Throw or take 4d6 damage and grappled.

Grappled creature can free itself by contesting Strength Check with Big Boy.

Fire Storm. Big Boy spins itself and burst fire and oil in 10 ft sphere radius centered on itself. Any creature in the radius makes DC 15 Dexterity Saving Throw or take 3d6 Fire damage and caught on fire. The creature that being grappled by Big Boy will automatically set on fire.

On successful save, they take half damage and does not caught on fire.

If a creature caught on fire, roll 1d10 fire damage at the start of their turn until they make effort to put off the fire.