Guide:Skeletron Prime strategies

Skeletron Prime, the Hardmode version of Skeletron, is intended to be the most difficult Hardmode boss, at least before 1.2. His high health, defense, damage, and multiple limbs will take a lot of punishment, and his limbs have the added effect of blocking non-piercing shots aimed at his head.

Terrain preparation
As with all bosses, an arena made out of Wooden Platforms greatly increases your mobility. You will want 10-15 rows of Platforms, each around 50 or so blocks long. The platforms should be suspended off the ground, to prevent the Prime Cannon's grenades from ever detonating. A solid ceiling should be avoided, since Skeletron Prime will often retreat a fair distance when not using his spinning attack. Every 5 or so rows, replace the centremost Platform with a solid block of any kind, and place a Campfire and a Heart Lantern on it. These two items will greatly boost your health regeneration up to 10 hearts a minute, even while moving. As with most bosses, starting the battle as soon as the sun sets will provide the maximum amount of time to beat Skeletron Prime, which is vital since defeating him can take all night. If you do not, he will transform into Dungeon Guardian Prime, making him insta-kill you and take nearly no damage.

General
Adamantite armor or Titanium armor with your respective headpiece (e.g, the Adamantite Mask for rangers) is a good set. Accessories that increase your mobility such as the Spectre Boots or Wings of some kind are a must. As Skeletron Prime is considered to be the hardest Mechanical boss, by then you probably would have killed the other 2 Mechanical Bosses. Making Hallowed Armor is a great choice. If you don't have enough Hallowed Bars, you can try to kill The Destroyer again. If you can, farm the Wall of Flesh to get your respective emblem, be it ranged, melee, magic or summoning (provided you're on PC.

For melee users, the Dao of Pow is an excellent one due to its long range and damage. The Ice Sickle fires a spinning scythe projectile that will pierce Skeletron Prime and can be acquired from mobs in the Underground Snow biome. Some type of spear weapon, ideally the Adamantite Glaive or Titanium Trident, can hit it if you get close enough. You can also use the Bladetongue which fires an Ichor projectile provided you can get close enough to it. Multiple Light Discs can be helpful with their high range. You can get Frost armor which boosts your damage and can inflict the Frostburn debuff. The Flying Knife is quite hard to acquire (being a rare drop from Hallowed Mimics) but it does not require to be in close quarters for full damage.

For ranged users, you can get your hands on the Adamantite or Titanium Repeater which are easily obtained. Combine them with Holy Arrows for acceptable damage rates. However, there are better alternatives; the Clockwork Assault Rifle is a burst-fire weapon with high speed which is complimented by Crystal Bullets. The Daedalus Stormbow is extremely powerful - especially when combined with Ichor Arrows or Hellfire Arrows - but quite hard to acquire, being a rare drop from Hallowed Mimics. If you have defeated The Destroyer, you should definitely consider the Megashark due to its insane speed and respectable damage. You can get Frost armor which boosts your damage and can inflict the Frostburn debuff.

Magic users can use the Crystal Serpent which functions similarly to Crystal Bullets and deals high damage. The Crystal Vile Shard deals somewhat low damage but can be used to hold Skeletron Prime's limbs in place, which allows the damage to stack up if you keep firing. The Meteor Staff is extremely powerful and easy to craft, provided you have some leftover Meteor bars from Pre-Hardmode. The Golden Shower deals little damage but inflicts the Ichor debuff even when it is switched away, allowing your other weapons to deal even more damage.

Summoners can use the Optic Staff to summon miniature versions of The Twins. You can also use the Deadly Sphere Staff to summon Deadly Spheres. There's also Pirates from the Pirate Staff, but those lack the ability to fly. Adamantite armor nor Titanium armor have helmets that boost summon damage but you can brave the Spider Nests for Spider armor which is designed exclusively for summoners.

Potions
Bring along 10-15 Greater Healing Potions (don't even consider regular Healing Potions, you should have made some of the Greater variety already). Mobile users can also use Horn 'o' Plenty if you have beaten Turkor the Ungrateful. For buff potions, the classic trio of the Swiftness Potion, the Ironskin Potion and the Regeneration Potion will do you a world of good. Endurance Potions will compliment the defence boost of the Ironskin Potion. Rangers with Bows should bring along an Archery Potion or two. Mages should use Mana Regeneration Potions and Magic Power Potions. Damage increasing potions like the Rage Potion and the Wrath Potion are good for everybody.

The battle
Skeletron Prime is a flying boss that consists of five parts: If you take out his head, you have killed the boss.
 * Prime Saw, a melee arm, with 8000 health.
 * Prime Vice, a melee arm, with 8000 health.
 * Prime Laser, a ranged arm that fires lasers, with 5000 health.
 * Prime Cannon, a ranged arm that fires grenades, with 6000 health.
 * Skeletron Prime, the head, with 28000 health.

Each limb has its own unique attack pattern, listed below. Although killing the limbs is not necessary, they can block the head (especially Prime Saw and Prime Vice), and destroying them can make the fight much easier. It's suggested to spend half the night attacking its limbs, then the other half attacking the head.

Prime Saw
Prime Saw is Skeletron Prime's most prominent melee attack limb, and the one that will do the most damage of any limb. At regular intervals, it will chase down the player, causing serious collision damage each time it hits. The arm can move as fast as the player can with Spectre Boots, and will accelerate in short bursts so it can catch up. It will eventually pull back to the head, waiting to repeat the cycle.

As it does a lot of damage, this arm should be destroyed first. By using the wooden platforms to change height when it charges, or with great speed, Prime Saw's attacks can be avoided until it is destroyed. Using the melee set bonus will help mitigate damage taken, after which the ranged set can be equipped.

Prime Vice
Prime Vice is Skeletron Prime's secondary melee arm. Though it will occasionally chase the player, it is more common for the arm to simply charge directly at the player, retract, then attack again. This arm is relatively easy to dodge, making it a minimal threat to an agile player.

Prime Laser
Prime Laser will consistently remain above the player, firing one laser every second or so. The lasers aren't as damaging as melee attacks and can be avoided fairly easily, but are harder to dodge if attempting to damage the head. Its low defense and health make destroying it much easier than the other limbs, so it may be worth removing simply to make the head easier to target.

Prime Cannon
Prime Cannon fires grenades at a rate faster than Prime Laser, which also do more damage. However, these grenades only detonate on contact with a solid block. In a wood platform arena, this effectively renders Prime Cannon a nuisance that occasionally blocks attacks. Leaving it intact buys more time to defeat the head.

Skeletron Prime
Skeletron Prime is the head, which must be destroyed to win. Skeletron Prime will try to float above the player at all times (use this opportunity by shooting the head from below), high enough that he may be entirely off-screen at lower resolutions. He'll close in to do his spinning attack, which doubles his attack and defense. Once he finishes spinning, he'll retreat again. If the head is not destroyed by morning, it will be locked in its spinning attack, gain a speed increase, and its attack and defense will increase to near-unbeatable levels. In this state, a single hit will kill the player, while the head will only take one or two damage per hit.

When trying to destroy the head, it helps to have destroyed at least two of its limbs first, ideally one melee-based and one ranged-based. The remaining two usually won't block too many of your shots. If all of the limbs but his head have been destroyed, he becomes incredibly easy. His attacks are relatively simple to dodge, and though he can cause a lot of damage, getting hit once or twice isn't a very big deal since he doesn't attack too frequently. The wings and Spectre Boots make it almost impossible for it to hit you.

When Skeletron Prime stops attacking and tries to retreat, chase it down using the wings. Though they'll eventually give out, you'll do a fair amount of damage on the way up. The head will come back down fairly quickly. Attack the head constantly and it should be destroyed before morning.

Caution: Even with the best armor and defense possible, Skeletron Prime can still easily kill you, as the head's damage while spinning can only be reduced to 53.