Is tizanidine addictive?

Always addictive.

Mushrooms are no more additive than any other foods. The hallucinogens found in some mushrooms may become psychologically additive to those will little or no will power or self discipline.

In forms yes, it is usually added to cocaine to create the feeling of numbness

Anything can be addictive; yes.

It has a powerful material from a plant called the diddly squat tree.