With story mode you can upgrade Tank, Briggs, Proof and Spider, to get all the skills of these guy's you only have to clear the survival mode. You'll have to face 37 enemy's at maximum. If you finished it you'll get 100.000$ which you can use to upgrade the guy's. Hint: every time you finish D-mob ( with a submission or K.O.) you get 100.000$, so you can upgrade the next person.