Skeletron

Skeletron is a boss which can be 'summoned' by talking to the Old Man in front of a Dungeon at night. The Old Man will turn into Skeletron immediately and start attacking you, so be prepared when this happens.

When you defeat Skeletron, you will gain access to the Dungeon. If you try to go into the dungeon by going through the door or digging yourself in without defeating Skeletron first, he will constantly spawn heads that will chase you throughout the dungeon. During the day these will insta-kill you, at night however they will do the standard damage as if you were fighting him as a boss. Note: If day breaks while you are fighting him normally, he will revert into a skull and insta-kill anyone near him.

How to defeat him
A good way to defeat Skeletron is to have someone use the Grappling Hook or the Ivy Whip to climb up the roof and having the rest positioned far from each other so the damage output of Skeletron is minimized, having ranged out of his reach and having 1 or 2 people hitting him with (melee) weapons while being close to him so your party's damage output is maximized, while Skeletron's damage output is minimzed.

You should also bring healing items like Glowing Mushrooms and Lesser Healing Potions with you and share with your party to minimize the damage output of Skeletron.

Health points
In the outdated leaked version that was used in most lets plays, Skeletron only had 4000 heath points. In the new version however, Skeletron is seen to have 6000 health points, and because of this, he is easily the hardest encounter in the game.

Head
He will spin his head when you are close to him, while he spins his head he will charge at you for 3-6 seconds. Resulting in lots of damage taken if you get stuck in a corner, since his head has a average reach and his speed is higher than your default speed. (note: Skeletron can also not be outran by the Hermes Boots, even when on full speed.)

Hands
He will flail with his hand when you are not in melee range of his head. This attack deals less damage than when attacking with his head, but he will have more range to attack you that way.

Respawn
You can only beat him once, if you have beaten Skeletron then the Old Man won't show anymore. Which gives you access to the Dungeon. But if you fail to defeat Skeletron you have to wait one day and talk to the Old Man again when it's night.

Confirmed Loot
[NEEDS EDITING] -Pandaturds
 * Crystal Heart
 * Copper Coin
 * Silver Coin