Describe how your friend plays. Does he drown you in projectiles, or is he more of a sword master? A lot of Toon Link players like to overuse his F-smash and D-air. Both are very easily sidestepped and punished with neutral-A combo or F-tilt. The F-smash you have to be able to predict, but once you've avoided it, he's pretty much screwed because most players typically go for the double-swing.
If it's projectiles you're having trouble with, then you have to get tricky yourself. I find that alternating spamming grenades, Nikita, and mortars (when they're close or trying to approach) works pretty well. I've yet to see anyone except Zelda (Din's Fire -.-) who can out-ordinance Snake. Once you're in your explosives-spamming mode, it only takes them to get caught in one explosion for you to be able to rush in with physical attacks and take control.