nuclear throne
Skeleton

Skeleton is a secret character playable only if you lose all of your HP as Melting while inside a Necromancer's resurrection circle. He's a very difficult character to play, as his "passive ability" is purely detrimental and his active gambles his health in exchange for not using ammo.

Features

Upon losing a fatal amount of HP within a Necromancer's summoning circle as Melting, you will be instantly turned into Skeleton, and the following things will occur: All previously acquired experience (radiation) will be removed, your character's level will be reset back to 1, thus all previously picked mutations will be lost, and your max HP will be set to 4. However, the weapons as well as the total ammo that you had prior to turning into Skeleton will be kept, and the game's difficulty and your kill count will stay the same.
Aside from spawning with 1 out of 4 HP, Skeleton is also less accurate (spread multiplier 1.5x) and has noticeably lower movement speed.

Special

Skeleton will fire a shot that won't use ammo and rads. There's a random chance that he takes 1 damage. The chance depends on what type of weapon you use — mainly how much ammo it uses per shot and how much ammo it receives from Mini Ammo Chests. This ability doesn't work if you hold a melee weapon that doesn't use ammo.
The chance that Skeleton takes 1 damage when firing a weapon with Blood Gamble equals:
If you have a Machinegun (ammo used = 1, ammo drop size = 32) and your other weapon is a Super Bazooka (ammo used = 5, ammo drop size = 6), then:
Which means Skeleton will be damaged more often with weapons that use a high amount of ammo per shot. With some weapons (Super Flak Cannon, Super Plasma Cannon), Skeleton is guaranteed to take damage if he doesn't have Throne Butt.
Blood Gamble ignores automatic weapons' continuous firing. It's always a single shot or a single burst, regardless of the weapon.

Throne Butt

Throne Butt adds an additional 1/3 chance that Skeleton won't take damage with Blood Gamble from a roll that would usually fail.

Ultra Mutations

Skeleton A

Redemption

Turns Skeleton back into Melting. Every mutation you picked while playing as Skeleton will be removed. You'll be able to pick nine new ones (standard eight and one extra) and one of Melting's Ultra Mutations instead.

Melting will have base 2 HP as opposed to Skeleton's 4 HP.

Skelly B

Damnation

Firing a weapon with Blood Gamble will reduce that weapon's reload time by 80%. This only affects the current reload; it is not a permanent reduction.

Gameplay

In the late game, Skeleton's active ability synergizes very well with mutations such as Trigger Fingers, Bloodlust, Throne Butt, and Damnation. This is especially helpful with weapons with high ammo costs (Super Plasma Cannon, Lightning Cannon, Super Flak Cannon, etc.). The high reload speed combined with the Bloodlust procs makes its active ability very effective against crowds. Turning back into Melting with Redemption is also a good tactic, which gives it an extra mutation, and if you have Crown of Death extra health.
Useful mutations:
Useful crowns:

Trivia