The Glitch

Wikia won't let me upload the image. Oh well.

The Glitch
The Glitch is a Hardmode Post-Golem Boss that can be summoned using the Virus Detector with a SystemHACK (bought from the Scholar NPC for 20 gold coins) at night. Or he can be summoned naturally, with the message, "Terraria has unfortunately run into a glitch...", this message can only appear if the following criteria are met
 * 1) The World is in Hardmode
 * 2) The Glitch hasn't already been defeated
 * 3) The Wall of Steel hasn't been defeated
 * 4) The three mechanical bosses, including Plantera and Golem,have all been defeated.
 * 5) The players defense is higher then 56

The Fight
When the Glitch spawns, it has two forms, in total the glitch's HP is 90,000 with a defense of 32. (120,000 HP and 35 defense in Expert) In it's first form, it hovers above the player slowly, spawning homing computer chips, also changing it's color as the fight progresses. when it reaches 60,000 HP (90,000 in Expert) it will begin shooting green lasers that inflict the Cursed Inferno debuff and red ones that inflict the On Fire! debuff, when it reaches 40,000 or below (50,000 in Expert) it will go into it's second form, where it has colors all over it's face and an angry expression, the Glitch now shoots colorful lasers that inflict no debuff, but can deal a LOT of damage if the player isn't careful. The Glitch will fire these more rapidly as it's health goes down, sometimes firing at the rate of the Megashark. The Computer Chips will also be replaced by Anonymous Minions, who always drop hearts when defeated. The Glitch and it's Computer Chips and Anonymous Minions are immune to the Poisoned, On Fire!, Venom, and Cursed Inferno debuffs.

Expert Mode
In Expert mode, the glitch and it's minions have more health and damage output, and it also has a new trick up it's sleeve, the fight won't be that much different in the first form but in the second form, The Glitch will try to position it's self close to the player, then ram into the player at a high speed, the lasers DO inflict the venom and confused debuff in the second stage, so if you can hold out against it, the loot is yours.

Drops
HackSword (11.2%)

Dimension Shard 5-10/EXPERT:10-20 (100%)

Computer Piece (1%) (Summons a mini version of the Glitch that will fight for you)

In Expert Mode:

Treasure Bag (The Glitch) (100%)

(Contains all of it's normal drops, plus the MapTeleport(allows you to teleport anywhere on the world map))