Skeletron Prime

"You feel the air getting colder around you..."

Skeletron Prime is a Hardmode Mechanical Boss which is essentially a harder version of Skeletron. It is summoned with the Mechanical Skull at night. Players have until dawn to defeat it. Skeletron Prime can also randomly spawn at dusk in Hardmode if it has not yet been defeated, in this case signaling its approach via the status message, "The air is getting colder around you..." or "You feel the air getting colder around you...".

The boss music is Boss 1, making this the only Mechanical Boss to share boss music with its Pre-Hardmode variant.

Attacks
Skeletron Prime has four limbs which are all immune to the Poisoned and On Fire! debuffs:
 * Prime Cannon fires bombs that do not destroy blocks, usually up into the air rather than directly at the player. It usually stays above the player.
 * Prime Laser shoots red Death Lasers similar to those of Retinazer and The Destroyer, and is always pointed at a player. It usually stays horizontal to the player
 * Skeletron Prime's Prime Saw and Prime Vice both act similarly to the The Twins when they are charging, but the Prime Laser acts similarly to Retinazer or the Wall of Flesh while shooting laser beams.
 * Prime Saw usually remains under the player, then swipes upwards or downwards.
 * Prime Vice will swipe around wildly, making occasional lunges at the player. It usually remains diagonal to the player.

Skeletron Prime will occasionally enter a "Rage Mode," in which its attacks become more aggressive:
 * Skeletron Prime's Head will grow spikes and start spinning towards the player slowly. Damage and defense is doubled.
 * Prime Cannon will aim at the player directly and fire rapidly.
 * Prime Laser will fire more frequently.
 * Prime Saw will begin homing directly towards the player's location.
 * Prime Vice becomes more aggressive and frequently lunges towards the player.

Prime itself is much more mobile than its predecessor, and will regularly move off-screen, which can make it difficult to hit reliably with ranged weapons.

Like Skeletron, if it is not beaten by dawn it begins to continually headspin like a Dungeon Guardian, dealing enough damage to kill most players in a single hit and having 9999 defense. During this time, it travels at a speed of 65 mph.

Tips

 * Using Frost armor is recommended due to Skeletron Prime not being resistant to the Frostburn debuff.
 * Standing on platforms far from blocks can mostly nullify the effects of the Prime Cannon, as its projectiles only detonate on blocks, while passing through platforms 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.
 * Although it is a little more time-consuming, focus the arms first. Once Skeletron Prime's head is no longer blocked by anything, the fight gets a lot easier.
 * Investing some time after the fight, defeating Skeletron Prime can be very profitable. It drops Souls of Fright, which can be crafted into Naughty Presents to summon the Frost Moon, and Hallowed Bars, used in the Pumpkin Moon Medallion which summons the Pumpkin Moon. Both events usually net a large amount of dropped coins.
 * Using Ichor weapons can be effective because of his high defense, however, it's best to switch to the Ichor Weapon then switch back again quickly, as they don't deal that much damage.

Trivia

 * Skeletron Prime will open and shut its mouth for the entire battle. This, however, has no effect in battle.

History
Skeletron Prime 机械骷髅王