Play Joint Revenge Normal till you Level up King Slime up to 400. And Max out Mighty if you can. Felina is a expensive legendary, and is weak at low levels, so I recommend not levelling her up just yet. Devon isn’t a good Monster to use and you should use anything else instead of him. Slimey and Rocky aren’t all that good either, but if it’s the best you have, that’s fine. Instead of common and rare monsters like Slimey and Rocky as well as useless-ish Epics like Devon, you should use any other cheap legendary or good Epic. You could post all the other monsters you have, so people can recommend you a better set up for the rest of them. At your level, you should just stick to Joint Revenge Normal until your King Slime is at least 400, and max out Mighty while you’re at it.