Horror takes the shape of an amorphous radioactive energy being that can turn radiation into a deadly beam, which can be used offensively and defensively. It's similar to the palace guardians but it has free will.
- Horror's passive gives it the option of an additional mutation choice every level up. Instead of the normal four per level, a fifth is added on the far right. Horror also has an additional ultra mutation to choose from, giving him three instead of the standard two.
- Horror's special shoots a green beam of tightly packed particles, using your Rads (experience) as ammo. The experience usage does not dip into previous levels; that radiation was already used for mutations. Each particle does one damage, that means 30 damage per second. The beam gets wider the longer you shoot it. It can also destroy enemy projectiles. It can't be deflected by Shielders or Crown Guardians.
- Enemies killed with the beam will drop back all rads you used to deal damage, to refill your meter up to its original state. Destroyed props or killed enemies that normally don't drop rads (like the I.D.P.D. or Small Green Rats) will drop radiation if damaged by the beam. Shooting a Proto Statue with the beam charges the statue with radiation. When the beam hits a wall the used radiation is lost.
- Using Horror's radiation beam for extended periods of time heals you for 1 HP every 2.5 seconds.
- The concept of Horror's passive is very helpful, as it gives a higher chance to have all your relevant mutations to build around any weapon. Its special can be a potential game-saver, being able to kill enemies after you run out of ammo. The beam can also destroy projectiles, making Horror have an easier time in areas where one would be under constant projectile fire (such as the Scrapyard and The Palace). Shooting a Proto Statue with the beam charges the statue with radiation. Thanks to its passive ability taking the Crown of Destiny leaves you with a choice between two mutations. Horror begins to shine once it reaches the late game, as it is either at the level cap or has all the mutations it wants, allowing it to use its active with relative freedom, as long as it has enough radiation to spare. This means that along with its beam and weapon fire, Horror can output a lot of damage in a very short time. If you have the Throne Butt mutation firing the beam against a wall for extended periods of time heals Horror if you're willing to sacrifice some radiation in the process, but this tactic only works when you have enough radiation to spend, which is on later character levels.
- Useful mutations:
- Throne Butt - rewards you with health for killing enemies with your charged radiation beam.
- Euphoria - gives you more time to aim your radiation beam at incoming projectiles to destroy them.
- Plutonium Hunger - assists in recovering scattered rads.
- Scarier Face - reduces the number of rads you have to expend to kill an enemy.
- Horror has no gender. It is a sentient being made of compressed rads.
- Upon death, Horror explodes into rads and radiation chunks.
- Its mouth is a portal just like the Palace Guardians have, but Horror hides it behind teeth. Horror is ashamed of it.
- Horror's B-skin resembles the purple portals that appear after you clear an area. The B-Skin also changes Horror's beam projectiles color to purple, that includes the projectiles fired after enemies die with one of Horror's ultra mutations.
- Between update #38 and #46 Horror started with the Rusty Revolver.
- As of update #48, Horror has its own voice.
- Before update #53 Horror's Throne Butt turned all Radiation Canisters into Big Radiation Canisters.
- Before update #57 upon contact with walls the beam particles would drop rads. When the beam hit an enemy the radiation was lost. It was then changed to be the other way around.
- Horror was implemented in update #34.