Slimetank works amazingly well with Persephia. Persephia’s rockoid summons usually spaces out your own stun protection way too much. But slime keeps it in play and offers amazing support. As throw next fodder or simply by staying in the game. As an absorber, purifier and protector 
(emoji because it’s 20% protect) it offers a lot.
Today I grinded a win by killing a full health Sturg Moth and Unicera just with slime and shiny fox using AOEs and stun killer lol.
I think a FL or mid game Slimetank is too risky, but endgame if you’re running lots of stun prone monsters back to back Or have monsters like Persephia that can space your own monsters out more, it’s very useful.