User blog comment:RRK/Skeleton/@comment-4726862-20120104021122

You NEED 200 health atleast to kill him, not that you will get oneshotted once you summon him without it, you literally NEED it in order for the "Curse" (the once that makes the Old Man turns into Skeletron), and I'd recommend 400 health. I killed him with 400 Health, Shadow armor full, 40 mana, an Enchanted Boomerang and Light's Bane (the shadow armor sword).