This is any liquid/slime/sludge form of Applied Phlebotinum that causes living creatures that touch it to somehow mutate or transform into... something else. Occasionally, it may need to be ingested (or injected) to take effect, but in most cases it can be easily absorbed through the victim's skin -- their own Lego Genetics will take care of the rest. The goo comes in many forms -- it may be toxic nuclear waste, some form of alien bodily fluid, mud from a cursed swamp, or contaminated water carrying The Virus. Examples of Mutagenic Goo include: