Blessing of The Pig (Recharges after a short or long rest). If you were to drop to half your hit points, you instead reset to your full hit points. You the gain a +10 to all damge you do and a -10 reduction to all damge taken.

Fly By. When you fly past a creature, you don't provoke opportunity attacks.

Magical Attacks. The pig's attacks count as magical for the purpose of overcoming immunity to non magical attacks.

Power Surge (2/Day). When you use your legendary action, you may use this feature to use the same action twice.

Running Attack. If the pig moves at least 30ft (flying or walking) before hitting a creature with a headbut attack, it deals an extra 13 (2d12) bludgeoning damge.

Multi Attack. The pig makes 3 attacks, one has to be its headbut.

Headbut. Melee Weapon Attack: +15 to hit, reach 10 ft., 1 target. Hit: 41 (4d12 + 15) bludgeoning damage. If the creature is large or smaller, it must succeed on a DC 25 strength saving throw or fall prone.

Powerful Legs. Melee Weapon Attack: +15 to hit, reach 10 ft., 1 target. Hit: 41 (4d12 + 15) bludgeoning damage.

Cloud of Gas. The pig cuts the cheese. All creatures (apart from itself) in a 300ft sphere must make a DC 28 constitution saving throw. A creature failing the save takes 128 (12d12 + 50) necrotic damage and 48 (5d12 + 16) psychic damge. A successful save means it takes half as much damge.

Fart. The pig makes one Cloud of Gas attack.

The pig has 3 legendary actions that it can take after any other creature's turn. It regains expended legendary actions at the start of its turn.

To Many Beans For Breakfast  (Costs 3 Actions). The pig makes 2 Cloud of Gas attacks. 

Enter the description for how mythic actions work for your monster here.

Mythic Action Name (Costs # Actions). Enter the description for your mythic action.