Never have I ever heard of killer zoas or mushrooms. Ricordeas can be semi-aggressive, but they are about the only one I can think of and its an absurdly rare case at that.
Toxic green palys can release a toxin onto your skin and if you cut open a zoa and get the fluid in your mouth/eyes you can get really sick, but again, both are extremely rare cases. I have heard of a certain zoa being a better and more aggressive grower then those around it and they overrun them, but thats more things like GSP and blue clove polyps.
Before you just say, Wrong. How about some evidence that supports what you are saying?