Oh, no... I'm talking about a type of slime that loses about ten-20 percent of its mass when it sleeps, sweating out the water and condensing itself while forming a thin, hard shell.  What is inside that shell is about as easy to detonate as nitroglycerin.  So, if they are attacked while they sleep... boom.  Of course their properties while awake would be notably different.  I'm thinking that these would be a savage variety only... at least at first.

Though, they would be a source for ideas regarding either explosive spit or other such variants on species' existing skills.  After all, none of these monsters have modern world knowledge to draw on.  It's a little harder to stay in character if your character doesn't have any believable reasoning path to connect their origin to where they're going or what they're figuring out.