Bellerophon

Spellcasting. The bellerophon is an 15th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 17, +9 to hit with spell attacks). The bellerophon can cast fly, wild cunning, chaos bolt (in the form of giant needles) and absorb elements at will and has the following spells prepared:

Cantrips (at will): true strike, Thaumaturgy, infestation, sapping sting, booming blade

1st level (4 slots): Bane, compelled duel, grease, hunter's mark, Tasha's Caustic Brew, magic missile (in the form of giant needles that deal acid damage)

2nd level (3 slots): earthbind, enhance ability, hold person, melf's acid arrow

3rd level (3 slots): slow, meld into stone, blinding smite, vampiric touch, phantom steed (can be cast as a reaction)

4th level (3 slots): vitriolic sphere, blight, polymorph, staggering smite

5th level (3 slots): contagion, hold monster, destructive wave, steel wind strike

6th level (1 slot): harm, disintegrate, flesh to stone

7th level (1 slot): regenerate

8th level (1 slot): animal shapes, Holy aura (the negative effects of the aura only effect monstrosities and simics)

* Immediately after casting a spell, the DM can have the bellerophon roll a d20. If it rolls a 1 or 19, roll on the Wild Magic Surge table to create a random magical effect.

Multiattack. The bellerophon makes two attacks: one with its lance and one with its hoof.

Adamantium Lance. Melee Weapon Attack: +9 to hit, reach 10 ft. Hit:  (1d12 + 2) piercing damage and (1d6 +2) acid damage. If the bellerophon moves 10ft or more to make a lance attack on a target, it can choose to continue moving 10ft. or more without provoking an attack of opportunity.

The adamantium lance deals double damage to structures. Also, it ignores AC granted by a shield or armor. On a critical hit, the lance attack will destroy any non-magic shields or heavy armor.

Once per turn when the bellerophon rolls damage for its lance attack, it can reroll the weapon's damage dice and use either total.

Mule Kick. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. (2d8 + 1) bludgeoning damage. If the target is a Medium or smaller creature, it must make a strength saving throw (DC 17) or be knocked prone. If the target is prone, the bellerophon can make one stomp attack against it as a bonus action.

Stomp. Melee Weapon Attack: +9 to hit, reach 5 ft., one prone creature. Hit: 22 (3d10 + 6) bludgeoning damage

Jittery. Other creatures provoke an opportunity attack from the bellerophon when they enter its reach.

Equestrian Body. The bellerophon has advantage on melee attack rolls against any unmounted creature that is smaller than it.

Faster Than It Looks. If the bellerophon is subjected to an effect that allows it to make a Dexterity saving throw to take only half damage, it instead takes no damage if it succeeds on the saving throw, and only half damage if it fails.

Nightmarish Persistence. The bellerophon's speed is not effected by difficult terrain.

Monster Hunter. The bellerophon's melee attacks have a bonus +3 to attack and damage rolls against monstrosities or simics.

Entropic Murders. Any creature slain by the bellerophon instantly begins to liquify, the process completing within a minute, leaving behind meaty goop behind that produces a stinking cloud