Well, with Envy's 2 wheels he'll be more maneuverable then me. I'll have more pushing power, but he'll be able to outmaneuver me if I try to get around to his side. Therefore, I'll ram him from the front. Hopefully I'll drive right over the top of Envy, and use the brief second to get under the back and ram into him. If this doesn't work, attack Envy at the sides, and wait for him to run out of gas. Overall, since neither of us has a damaging weapon, the damage category isn't really important. Overall, be aggressive and controlled.