I definitely like this Slime Master after my first reading of it, and look forward to running it. I think I need to examine it more before I give real feedback, but I do have some preliminary questions and suggestions:
You treat your slime guardian as an eidolon, does this include for the purpose of equipping magical items? As in, if you find a way to gear it up, it takes away from the Slime Master's own magic item slots? How about feats that affect eidolons?
Also, the Impact abilities lack save DCs. I think that instead of defining just the flightbreaker's DC, you should state that all Impact abilities use that DC formula. Currently, the later Impact abilities seem to lack language stating what their DCs are. It is pretty obvious what the intended DCs are, but it never hurts to have clarification.