Toxic Gas is an aura projected by the Brain Bug boss. It affects all CP Units, Heroes, and Buildings with 9 range, slows their movement, in particular slowing their movement while on creep, and deals 20 damage to units, 30 damage to heroes, and 40 damage to buildings every half-second. Toxic Gas deals +10 damage per tick on Hard, and +20 damage per tick on Insane and Mental (80DPS base, 100DPS to Heroes, 120DPS to Buildings). Damage from the gas counts as spell-damage and thus ignores armor. Predator can reduce the damage by applying Demoralize to the boss. Units taking damage from the aura have the Toxic Gas debuff placed on them. Toxic Gas remains on targets for 2 seconds after they leave its application range, continuing to slow and damage them.
Toxic Gas also appears during a World Event and will be emitted by certain structures.