These are all relatively easy to pull off and come from my own experiences (im not exactly a smash
g o d)
Down throw to f-air string is a classic
Full jab to PK Fire to f-smash seems to works at low percents
Down-tilt nearly combos into itself, but a good strategy i've found is down-tilt into down-tilt into dash-attack. This can lead into aerial strings or a landing punish.
Up-smash is great for shield pressure and near the ledge can lead into an aerial string (Seriously, ive broken shields with this beast)
There's always the Pk Fire into PK Fire into PK Fire etc. if youre
that guy
Up-tilt to up-smash to back-air seems to work out well for me most of the time. At lower percents this can be proceeded with a dash attack into up-air as well.
Aerial PSI Magnet to falling up-air close to the ground has just enough hitstun/windbox to put your opponent off guard. (Seems true sometimes but definately is not) Can lead into itself, or grabs.
This last one isn't really a combo (heck, are any of these combos?) but its won me a few matches. Send up a PK Thunder, forcing your opponent to air dodge (This works best high from any platforms) Now that theyve spent their airdodge, you have 3 choices. 1) bring the thunder back to yourself and perform a PK Rocket, (works well if your opponent falls quickly or is near the stage) 2) kill the thunder and try to land a PK Flash (This one works for me the most), or 3) Kill the Thunder and move into an up-air/back air. Up-air, you start the cycle again. Back-air, if it sends them offstage go for a PK Flash or down-smash edgeguard. If not, go for f-air, PK Fire (only if theyre about to land) or you can try for an up-smash.
Oh one more thing, if your opponent tries to reflect your PK Flash, its not the end of the world. Most reflects have huge endlag and can end up meaning more damage to your opponent through an aerial combo or even an accidental self KO
NOTE: Most if not all of these can be DI'd from, and none of them are true combos. Bear that in mind and make sure to mix it up. Sometimes the patient punish can keep you alive and your opponent hurting more than an aggressive combo play.