Skeletron Prime

 is the Hard Mode equivalent of Skeletron. It is comprised of a head and four arms, each with different HP, power, defense and attack patterns. Just as Skeletron is one of the hardest pre-hardmode bosses, Skeletron Prime is considered one of the hardest bosses in the game. In total, he has 25,000 health.

There are two ways to spawn Skeletron Prime:


 * 1) If Skeletron Prime has not been defeated in a particular world, it will sometimes spawn at night on its own. If this happens, then it will be heralded by the message " You feel the air getting cold around you... " appearing at dusk. So long as the player is not underground, the boss will spawn shortly after this message appears.
 * 2) *If the player is underground when they receive this message, Skeletron Prime will spawn shortly after they reach the surface. If the player stays underground for the whole night, Skeleton Prime will not spawn.
 * 3) Using a Mechanical Skull at night will spawn Skeletron Prime.

When killed, he will drop about 20-40 Souls of Fright, 14 Gold Coins, and 5-15 Greater Healing Potions. He will also drop 20-30 hallowed bars and has a rare chance to drop a Skeletron Prime Trophy, or a Skeletron Prime Mask. Like Skeletron, the hands do not drop anything.

If all players are killed, Skeletron Prime will disappear underground. The only way to see him again is to summon him.

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Overview
Skeletron Prime is comprised of five individual parts: the head and four different limbs. This makes it the most complex monster in Terraria yet.

Skeletron Prime
This is the part with the most HP and is also the main part of the boss &#8212; when this part is destroyed, Skeletron Prime is defeated. Its attack pattern is the same as Skeletron: it will usually keep its distance from the player, but will periodically start spinning and lunge at them for increased damage and defense. However, unlike Skeletron, it grows spikes from its head when attacking, which give it a slightly larger range, so care must be taken to not get too close.

Prime Laser
The Prime Laser orbits around the head, shooting a low-damage beam at the player every time it is facing them. With 5,000 HP and a low amount of defense, it is the least threatening of the boss's weapons, although it is not to be underestimated. It will sometimes lock on to the player and shoot several beams in succession, so active dodging is recommended.

Prime Cannon
The Prime Cannon is slightly more resistant than the Laser (6,000 HP) and will periodically shoot prime bombs that deal average damage to a player (about 30 per shot with a full Adamantite set). Depending on its own state and that of the other limbs, it will start replacing the single shots with volleys of 3-5 cannonballs, so it is best to keep moving, especially when the boss is directly above the player. The bombs inflict the Debuff "Confused" and other ailments.

''Note: The cannonballs only explode on contact with a solid block, and will pass straight through Wood Platforms, so standing on an aptly-built line of them will render this weapon useless. Using a form of flying (Gravitation Potion, for example), will also allow you to avoid the cannon's balls.''

Prime Vice
The Prime Vice is Skeletron Prime's main melee weapon. When near the player, it will make a lunge at them. It has 8,000 HP and greater defense than the ranged weapons, and also has a rather large hitbox, so it will likely intercept part of the bullets shot at the head.

Prime Saw
The Prime Saw is the boss's most dangerous weapon. It has 8,000 HP, the most defense of all limbs, and its attack is a lunge at the player that, when it connects, scores a rapid streak of powerful hits. As long as the Prime Saw is on the field, extra care should be taken in order to prevent getting too close, lest the player quickly lose a lot health to this attack. A Cross Necklace can be used to lessen the damage done by this weapon due to the fact that it increases the duration of invincibility after being attacked.

Pointers and Behavior

 * Unlike most summonable bosses, Skeletron Prime will not despawn at dawn, but (just like Skeletron) will gain a huge defense and offense buff and will start to relentlessly chase the player (pretty much acting like the Dungeon Guardian), ultimately killing them in one blow. It is therefore best to summon him just after sunset (7:30 PM in-game). This way, they will have a maximum of 15 minutes to fight the boss.
 * Skeletron Prime will react to most attacks by backing away from the player, often off-screen so using fullscreen mode with a large resolution is recommended.
 * The Vice and Saw will briefly detach from the body whenever they attack the player: this is a good chance to score some hits at the head without the risk of the shots being blocked.
 * Like Skeletron, the hands' hitbox doesn't include the arms, so it is safer and simpler to just jump over them rather than completely move out of the way.
 * Avoid using explosives like Hellfire Arrows or Grenades; a melee attack could suddenly block the projectile and the splash damage could hurt you badly.
 * Each part of the boss can target a different player; This allows a team of players to split them up, causing them to spread out and become less effective.
 * Be careful using rapid-Mana costing weapons as you can run out of Mana very quickly. Always have an alternative like far shooting melee weapons (like Vampire Knives) or ranged weapons when you do.

Strategy

 * Since the battle can drag for quite a bit, it is advisable to wear the best pieces of armor available, since Skeletron Prime has a huge arsenal of attacks, it is likely that the player will take many hits during the battle, so maximizing defense should be the main priority.
 * Bring powerful ranged weapons; the Megashark will deal lots of damage quickly, while the Hallowed Repeater will let you exploit the buff from Archery Potion and use the special attacks of several arrows to quickly deal with all the parts. A Star Cannon can deal large amounts of damage, but would require a large amount of ammunition to be a viable option.
 * For magic users, recommended spells are Golden Shower, Crystal Storm, Nimbus Rod and Cursed Flame.
 * If you have the materials, try using Frost Armor, Golden Shower, 5-15 Greater Healing Potions, and a Megashark. Use Golden Shower to give the boss the Ichor Debuff and switch with Megashark for higher DPS. Repeat when the debuff wears off.
 * Other than attacking the player and blocking their way, the hands will protect the head against any non-piercing weapon: Holy Arrows, Crystal Bullets and/or the Cursed Flames spell are a good way to pierce through its defenses and damage the head and arms simultaneously.
 * Since Skeletron Prime tends to move back and forth relative to the player, it is best to stand ground in one place (preferably fitted with a heart/star generator) and go after the boss every time it is in range, then coming back down and waiting for it to descend again. Rocket Boots and Wings greatly aid this strategy.
 * Once the boss is down to one or no arms, the head can be easily finished off with a spear or flail, since they can score several hits per use and the head's movement is predictable enough.
 * If you don't want to make an arena, you could also try to fly around with Gravitation Potions and Wings while shooting Skeletron, which also makes it easier to visit the Nurse when necessary without risking her death. Summon Skeletron and fly around dodging.

Trivia

 * Skeletron Prime has a head and hands made of metal, while its arms remain made of bone.
 * The name seems to be a reference to Megatron and Optimus Prime from the Transformers franchise, as well as Skeletor from the He-Man television series.

Bugs

 * It is possible that when he dies, Skeletron Prime will vanish, not drop anything, and his limbs can still be attacked for a few seconds despite him being dead.
 * Rarely Skeletron Prime will not spawn when the player has used the Mechanical Skull or the icon The Air Is Growing Cold Around You has appeared
 * Sometimes at dawn, Skeletron Prime (Guardian form) will fly above you and make it easy to kill him with a sword, however you only do 1 damage.
 * Sometimes when fighting: The Destroyer, Twins, Ocram, and Skeletron Prime all at once he will dissapear.
 * Sometimes while wearing the Turtle armour at dawn he rushes the player, doing 9999 damage, but, due to the Turtle Armor's high Thorns Effect, Skeletron Prime will also die, and drop the items, even if he has 9999+ health.
 * Sometimes when flying up to world height and making Skeletron disappear above the screen, Skeletron Prime will lose all his body parts except for his Saw.