Special Trait Name. Invulnerability to non-magical damage, and also damage of elemental types.

Spellcasting. 

Any spell the DM wants this demon to cast once per spell.

Bite: Kirby eats you, and you immediately take 50 damage. You also are now grappling Kirby's Tongue

Spinning Death: Kirby spins around, and kills anything within 15 feet that has less than 60 HP.

OOF: Whenever someone dies at Kirby's hand, Kirby eats them and regains 50 HP.

Roll: Kirby turns into a ball, and chases down a player, and the player has to make a DC 16 Dexterity save or Kirby uses Bite on you.

Star Shot: Kirby shoots a star at a player within 80 feet. If it hits, the player takes 10d10 fire damage, and is pushed back 30 feet.

Reactions: Burp: After eating someone, Kirby can spit out a bone at a player within 60 Feet, and the player must make a DC 17 Constitution save or be poisoned and take 30 damage per turn until either taking 35 fire damage, or until ANY healing items or spells heal over 20 Hit Points.

Jump on: Kirby, when engaged at first, jumps on a players head, and then starts choking them with his tongue, it takes a DC 17 Strength save or be held their, and take 50 bludgeoning damage. Each turn, the players are allowed to make a save on strength of DC 17, but then it increases by 1 difficulty each time you fail the save, and you also take an additional 75 bludgeoning damage, and the amount increases by 10 points of damage each turn.