Santa-NK1

Santa-NK1 (also known as Santank) is a boss that spawns during the Frost Moon event. When below half health, the face and beard of the Santa mask will be torn apart to reveal a morbid skull underneath.

Santa-NK1 continuously repeats three attacks consecutively:
 * First attack: Chain gun sprays bullets in the player's general direction.
 * Second attack: Presents launch high, then rain down via parachute from above, exploding on contact with players. These travel through blocks.
 * Third attack: Rocket barrage. These also travel through blocks.

While moving, it also drops large spiked balls on the ground that deal high damage (120-150+ with Chlorophyte armor). These increase in frequency as Santa-NK1 takes damage.

Trivia

 * "Santa-NK1" is actually a play on the word "Santank" (ie. Santa Tank), the name used when the enemy was announced (Santa-NK1 -> Santank1 -> Santank). It may also be a reference to Santa Claus' original name, "Saint Nick" (NK1 = Nick).
 * Santa-NK1's robotic Santa concept could be a reference to the Robot Santa Claus from Futurama.
 * Its arm appears to be the Chain Gun, which it sometimes drops.