Thanks for the response! I also often have trouble finishing off puff players. I've had some luck with utilt and dair when they are off stage. Is that the best way to go for kills? Or is there more efficent and safe ways?
I believe that the Puff MU is absolutely dominated by stage control.
Establish it, and maintain it for as long as possible. If the Puff is above you, you are in an advantageous position. If the Puff is in the corner, they will want to return to center stage and will not have as much space as you to work with. They lose many options.
Remember that when you have stage control and they are in the corner, a lot of Puff players will attempt to roll. Use low lag moves like SHFFL fair and dtilt so that if they roll, you can quickly turnaround grab WHICH CAN GET YOU THE KILL.
Okay, as you killing Puff, don't try to fsmash in neutral as she will punish you hard if you whiff it.
If she is in the air, the floaty killer (side-b to utilt) can be very good. But if they are on the ground, they will CC and punish you.
Learn your grab game on Puff!!!! Learn to Pivot Fsmash!
http://smashboards.com/threads/kadanos-perfect-marth-class-advanced-frame-data-application.337035/ (Scroll down until you get to grab game on Puff)
You will mostly kill her with tilts, specifically ftilt and utilt. But uair can also be used at higher percentages when they're above you, especially on stages like Yoshi's.
And obviously NTSC dair can be very reliably, but don't commit too hard, you might lose a stock if you do.
Something else, a lot of bad Puff players will try to Side-b at the ledge to get you offstage and convert the situation. If you see that your opponent does this, bait it and fsmash the f*cker.