By Dr Mike
Characters with MASS CONTROL are able to increase or decrease their density.
Increased density means higher strength, greater resistance to knockback and lower speed. The characters hit points also triple, effectively making them take 1/3 less damage than normal.
Reduced density menas greater speed and agility, with lowered strenght and hit points, and the character is much easier to knock back.
Change of density is accompanied by a black globule effect around the character.

Density change is achieved through INCREASE MASS and DECREASE MASS commands on the character or their portrait.