Well here's some general tips for the fox matchup: look for sneaky grabs, throws can lead to rests on bad di, or lead to edgeguarding situations which could easily result in a kill. If you are above a fox, ive found it useful to put out a nair and fastfall down, so that if they try to jump they will just hit their head. If youre close enough to the ground when you hit the fox with your nair, you can auto cancel-grab them. If a fox is running away from you lasering, unfortunately the smartest decision is probably to plank (if you are ahead) in all honesty, but you should only do that if youre a weenie and you dont think you can take them foreal. I'll usually just try to keep them in a corner (in fact I like smaller stages vs fox for this reason) by spacing bairs, and crossing up with nair-grabs every once in awhile. Up-airs under platforms is reeeally good. Also if they are rando up-smashing you, theyve probably caught on to your movement/landing patterns, so consider mixing things up like how many jumps, where you land, etc.Also I've found forward smash very useful n this matchup, if they are ever approaching you while youre on the ground, throw out a forward smash for the trade, itll be well worth. (you can also wavedash back before fsmashing for cleaner results.)
Just keep on thinking. Puff relies on out-thinking your opponent, and getting cheesy rests.