I bet it was TK or EE lol.
Anyways, the most important Ness specific techs IMO are pivot PK Fires, PKT2 bounce recoveries, PKF lag cancelling, magnet cancelling, and PK Jumping.
Pivot PK Fire is just dashing back, and PKFing forwards to manage spacing.
PKT2 bouncing involves hitting a wall so that you bounce, and PKT2ing again.
PKF Lag Cancel is using a dair after an aerial PKF to cancel the landing lag (see my guide for more details).
Magnet cancelling is a technique to diminish the lag on magnet after absorbing something. Upon absorption, tilt the stick down or sideways to spot dodge or roll, or jump to act out of the magnet. You can also usmash.
PK Jumping is DJ+PKF at the same time, which shoots you forwards, allowing you to move while casting PKF.
Outside of that, the most useful universal techs for Ness are proably usmash out of dash/shield, ledge trumping, and pivot grabbing.