I've created stats for The Rust for the RPG GURPS. In this version, the Rust starts out as a disease...Rust victims must make a HT-2 test every 2 hours or cough up blood, taking 1 hit of damage. Anyone who gets near the victim (or the blood) must make a HT-3 test or become infected, anyone who
touches the victim must make a HT-4 test, and anyone who touches the
blood must make a HT-5 test. Placing a thick cloth over your mouth and nose makes the test HT-1, and wearing a gas mask negates the test entirely.
Stage 1
Every week victims must make a Will-4 test or lose 1 IQ permanently as their sanity is eaten away and their mind is corrupted by Rust. The GM should keep track of how much IQ is lost in this way. (See the table below for the effects of the corruption).
| IQ Lost | Attributes | Disadvantages | Other |
| 4 | --- | Bad Temper | --- |
| 6 | +1 ST | Bloodlust | Hair turns white. |
| 8 | +1 Move | Berserk | Eyes turn red. |
| 10 | * | * | * |
*At this point the victim's mind has been completely consumed by the Rust. The disease moves into Stage 2.
Stage 2
Once a victim's mind is completely consumed by the Rust, the victim becomes a Kaibutsu. At first, the Kaibutsu looks just like the victim, but every 2 weeks, the Kaibutsu's Appearance drops by 1. Once the Kaibutsu's Appearance drops below Hideous, the Kaibutsu's form writhes; muscle, bone, and sinew shaping into a Mutation Form (Stage 3).
Kaibutsu gain +1 ST, +2 DX, -1 IQ, +0 HT. Kaibutsu lose all of their past Mental Advantages and Disadvantages when they rust. They also lose all their Mental Skills but retain their Physical Skills (because of muscle memory). A Kaibutsu with a Weapon Skill will wield weapons of that type, but only if it's a Melee Weapon. Kaibutsu have very small claws, which cause sw+1 cut damage. They also bite, doing thr-1 impaling damage.
The Kaibutsu will attack humans on sight. Anyone wounded by a Kaibutsu, but not killed, must make a HT-8 test the next day or be infected by Rust. Kaibutsu won't attack other Kaibutsu or Mutation Forms, but
will attack Stage 1 victims.
Stage 3
Mutation Forms are the Rust given shape. They are incredibly strong and fast and, despite their appearance, are very intelligent. They will stop at nothing to infect (or, failing that, kill) everyone in their path.
Mutation Forms don't cough up blood. Mutation Forms gain +5 ST -1 DX, +4 IQ, +2 HT, and +2 Move. Mutation forms lose all their past Advantages and Disadvantages when they transform. They lose all their Skills. They don't use weapons...they don't need them.
Mutation Forms will neither attack Kaibutsu,
or Stage 1 victims. Mutation Forms can smell The Rust coming from them.
Anyone wounded by a Mutation Form, but not killed must make a HT-10(!) test or be infected by the Rust.
