Skeletron Prime

Skeletron Prime is a Hardmode mechanical boss which is essentially a more difficult version of Skeletron. It consists of a head and four limbs, but, similarly to Skeletron, only the head needs to be defeated to defeat the boss.

Skeletron Prime can be summoned manually using a Mechanical Skull at night (7:30PM to 4:30AM). It also has a chance to spawn naturally at dusk once a Demon or Crimson Altar has been destroyed, as long as it has not yet been defeated at least once in the current world. If spawning this way, its arrival is announced by the status message "".

If Skeletron Prime is not defeated by dawn, it will behave much like a Dungeon Guardian: It will cease using its limbs and instead charge at the player at extremely high speeds, dealing usually lethal damage upon contact.

Behavior
Skeletron Prime's head constantly endeavors to remain between 31.5 and 12.5 tiles above the player and within 6.25 tiles of either side of the player. It can accelerate infinitely in order to move back into this area. The head does not actively attempt to make contact with the player.

Skeletron Prime's four limbs all have unique attacks:
 * Prime Cannon fires every 2.33 seconds that do not destroy tiles, usually up into the air rather than directly at the player. It usually stays above the player.
 * Prime Saw usually remains under the player, moving up and down.
 * Prime Vice will swipe around wildly, making occasional lunges at the player. It usually remains diagonal to the player.
 * Prime Laser shoots red Death Lasers every 3.33 seconds, similar to those of Retinazer and The Destroyer, and is always pointed at a player. It usually stays horizontal to the player.

Every 10 seconds, Skeletron Prime will enter a spinning phase for 6.67 seconds, in which its attacks become more aggressive:
 * Skeletron Prime's head will grow spikes and start moving towards the player at, exactly like how its pre-Hardmode counterpart Skeletron does. Damage and defense are doubled to /  /  damage and  defense. In , the base spinning speed is  and is increased the further the player is away, up to a maximum of  at a distance of 37.5 tiles.
 * Prime Cannon will aim at the player directly and decrease its cooldown between firing to 0.67 seconds.
 * Prime Saw will begin homing directly towards the player's location.
 * Prime Vice becomes more aggressive and frequently lunges towards the player.
 * Prime Laser will fire lasers every 1.33 seconds.
 * Skeletron Prime lets out a every time it enters the spinning phase.

Upon dawn (4:30AM), Skeletron Prime will enrage and permanently behave like a faster Dungeon Guardian, increasing its velocity and usually killing the player instantly if touched: its damage increases to 1000 and its defense raises up to 9999. It will remain in this state until defeated, even if it becomes night again. If defeated, it will drop items normally.

If the player is more than 375 tiles away, Skeletron Prime will start moving downwards and will quickly despawn.

Tips

 * Standing on platforms /  Planter Boxes far from blocks can mostly nullify the effects of the Prime Cannon, as its projectiles only detonate on blocks, while passing through those tiles harmlessly.
 * Unhindered movement is crucial when Skeletron Prime's head starts spinning, as it deals double the regular damage. Wings greatly aid in moving vertically, and flattened terrain or a sky bridge are convenient for horizontal movement. Fast mounts like the are useful as well.
 * Although it is a little more time-consuming, focusing on the arms first is very rewarding. Once Skeletron Prime's head is no longer shielded by anything, the fight becomes a lot easier. Prioritize damage on the arm which is causing the most damage or disruption, so it can be destroyed and removed from the fight as quick as possible.
 * A good idea is to focus on the Prime Laser first, as it is harder to dodge than the other limbs.
 * Due to Skeletron Prime's overall high defense, inflicting it with is effective, as it is not immune to it. Note that most Ichor weapons lack in damage compared to other weapons, so they should only be used periodically for inflicting the debuff.
 * In fact, as the head is immune to Cursed Inferno but not Ichor, Crimson world players have a clear advantage over Corruption world players in this sense.

Trivia

 * Skeletron Prime will open and shut its mouth for the entire duration of the battle, except for when its head is spinning. This is a purely cosmetic effect.
 * It is the only mechanical boss whose name contains the pre-Hardmode boss's name. Furthermore, it is the only mechanical boss to share boss music with its pre-Hardmode variant. Additionally, its name does not begin with the word The, unlike the other two mechanical bosses.
 * Unlike Skeletron, Skeletron Prime's defense doubles when its head is spinning.
 * Although Skeletron Prime's head is immune to Cursed Inferno and, its limbs are not.
 * Normally, Skeletron Prime's head has 2000 less HP than Plantera, but in and, they both have the same amount.
 * The Bombs fired by the cannon resemble the, with different coloring on one half.
 * Skeletron Prime is the only boss with more than two arms.