Blazing Behemoth

Rampage. When the behemoth reduces a creature to 0 hit points with a melee attack on its turn, the behemoth can take a bonus action to move up to half its speed and make a flaming punch attack.

Siege monster. The behemoth deals double damage to objects and structures.

Death Explosion. When the behemoth dies it explodes in a burst of fire. each creature within 120ft of it must make a DC 15 dexterity saving throw or take 10d12 fire damage on a failed save or half as much on a successful one.

Multiattack. The giant makes two attacks, using Flaming punch or Fireball Throw in any combination.

Flaming punch. Melee Attack Roll: +11, reach 10 ft. Hit: 24 (5d6 + 9) Bludgeoning damage plus 12 (4d6) Fire damage.

Fireball Throw.
Each creature in a 40-foot-radius Sphere centered a point of the behemoths choice within 80ft of it makes a DC 15 Dexterity saving throw, taking 5d6 Fire damage on a failed save or half as much damage on a successful one.

Legendary Resistance (2/Day) If the behemoth fails a saving throw, it can choose to succeed instead.

The behemoth can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The behemoth regains spent legendary actions at the start of its turn.

Punch or fireball. The behemoth makes a punch or fireball attack.

Flame Armor(uses 2 actions). The behemoth coats itself in flame for a minute. it's armor class increases by 3 and any time a creature attacks it, that creature must make a DC 15 dexterity saving throw or take 1d8 fire damage. the behemoth can only have this ability active once per minute