The Red King Greatsword is one of the many weapons that can be acquired from the Nightmare, a recently introduced 'domain' of the Ratboy's Nightmare Update. It can be purchased from the Green Golem or MANAGER SUPREME at a price of 5,000,000 gold.
In appearance, it is a very large sword with a wide red blade. It is held at the very end of the hilt, which has a rugged design and a mixture of red and gray colors. The blade ends in several sharp points resembling those of thorns and sharp blades.
Like all greatswords, the Red King Greatsword is slow and heavy to use, with its basic attack consuming 4 stamina per swing. While it is only capable of attacking once per second, the large blade easily allows each wide swing to hit multiple targets without issue.
The special ability of the Red King Greatsword is titled 'Blade of Rage', which, upon activation, spends 4 stamina and swings the blade once before raising it in the air and releasing its rage in a small explosion. The greatsword begins to emit red sparks of energy, and from the moment, it is ready to swing again. The player has 10 seconds to take advantage of the 705-damage explosive swings the weapon offers. The special ability's cooldown lasts for 28 seconds before it can be used again.
- The players can swing approximately 9-10 times with the Blade of Rage before it returns to normal, though the long special animation hampers the overall effectiveness of the attacks.
- The Red King Greatsword's special, along with the Honoring Blade, have the longest cooldown of any other special abilities in the game.
- The Red King Greatsword and the Wired Fury Set goes well together for vanity purposes.
- During the development of the Ratboy's Nightmare Update, its placeholder name was "Blade of Rage".
- During the Balance Update [v1.31], the Red King Greatsword's base damage was increased from 420 to 525 points.