Skeletron

Skeletron is the final normal mode boss in NTerraria. He is summoned by talking to the Old Man at the dungeon at night time and clicking "Curse". He must be defeated in order to enter the dungeon without being assaulted by Dungeon Guardians. Skeletron will perform one of two attacks:
 * 1) Float while he slaps you with his hands.
 * 2) Spin towards the player at a much faster speed. Hands do absolutely nothing. Defense is reduced to zero, take this time to use ranged attacks to deal as much damage as possible before he attacks you again.

It should be noted that Skeletron MUST be defeated before day time, or else his head gains stats identical to a Dungeon Guardian. He will spin indefinitely, even after night time comes. Any hit from Skeletron in this state would instantly kill even the tankiest of players.

Recommended items are: Cloud in a Bottle, Hermes/Spectre/Lightning/Frostspark boots, these items help you move around, so use these to avoid taking damage.