Just an idea: I may or may not actually write this as an SCP.
So, it's a yellow powder that comes in a small black box with one of those cartoonish lighting bolts on it's surface. You throw it at a surface at high speed, light it on fire, or wet it, and it turns into a glob of plasma that can be manipulated without harming anyone or any surface. However, if the "user" loses concentration, the plasma may revert to, well, normal plasma.
And we all know how kids are….
Doctor Wondertainment is not liable for any damages caused…. blah blah blah.