Old Man

The Old Man is a NPC found outside ALL dungeons. He guards the dungeons, and the dungeon cannot be entered until he is gone. When spoken to at day, he does nothing. When spoken to at night, he will turn into the Skeletron boss.

The Old Man will also become Skeletron's head and instantly kill you if you decide to go into the dungeon without fighting him.

The Old Man is not immortal and can be killed if trapped into a pool of lava. The Old Man takes 1 damage a second from the lava and after his 250 hp is depleted he is dead. Although the Old Man can be killed, his death does not eliminate the skeletron heads inside of the dungeon, additionally the old man does not respawn leaving no means of killing skeletron, or exploring the dungeon, without facing swift inevitable death.