I had a really hard time figuring this one out, so I thought some people might like to read it.
How to beat last boss:
Part 1: Hit him with your stick a few times. Try not to get shocked and avoid Skinny when he charges you. After a few hits, he will go back to the oil barrels to refuel. While he's refueling, hit him with a flaming stick.
Part 2: Hit him again with your stick a few times, except instead of charging you, Skinny will jump and send out shockwaves. Wait for him to refuel at the oil barrels and attack him with the flaming stick.
Part 3: Keep hitting him, this time he'll send out homing missiles which you just outrun. When he goes back to the barrel for a third time, hit him with a flaming stick and you will have won.