First off, practice recovery from any possible angle. Whether it’s straight up, the bottom corner, horizontally, or down, you want to get it so you always get the ledge grab. Recovering too high can result in a fatal punish if your opponent is good.
For me, side-b is mostly used for spacing. I use it in the air mostly so it goes diagonally. It keeps the opponent away from you so you can land safely.
I mainly use up-b for edge guarding (be sure to use the tail and not the head), and of course, recovery.
Since down-b can cause the opponent to flinch, I use it for spacing if they get to close. Down-b also stalls your jump, so you can use it to delay your landing and throw the opponent off timing.
Up-air got a new rework in Ultimate. It now has multiple hitboxes, and can pull opponents into it. It’s pretty good for killing at high percents, but your opponent can slip out of it.
Forward-air and back-air are pretty much about the same as in smash 4. Back-air can kill early at ledge, and forward-air can kill at really high percents.
Down-air has am increased sweet-spot hitbox now, so it is easier to spike. Down-air is also a viable option for combo starters, such as:
- dair —> fair (combos into fair)
- dair —> bair (read DI)
- dair —> uair (can kill)
Up smash has killing power now, so it would kill at around 100% or higher. You can also use it to edge guard your opponents by standing on the ledge (facing off the stage) and charging up smash.
Down smash can also be used to edge guard your opponents, but instead of facing out, you are faced away from the blast zone, at the edge.
Forward smash can deflect projectiles if you release at the right time. It also has a similar “tipper” effect that increases knockback if you hit the sweet spot.
Down throw can combo into fair. You can also land a dair somewhere in the combo if the opponent DI’s in.
Forward air is pretty good for getting your opponents off stage. That’s about all I use it for.
Up throw is pretty useless. Sometimes you can land a uair in there. You can use it to get your opponents off the ground I guess.
Back throw is Ness’ strongest throw. It can kill pretty early (about 80 or 90). At really low percents, you can back throw into fair or bair. Whichever works. However, it isn’t the strongest back throw anymore. Ness has been dethroned and Incineroar has the strongest back throw now.
I don’t really suggest spamming PK Fire. You could maybe get about 2 PK Fires in a row for easy damage. But any more than that, and you’re just being annoying.
I play in a passive-aggressive style. If there’s an opportunity to combo or get some damage, I’ll take it. If I’m losing by a stock or quite a few percent, I’ll play really aggressive, because if you stay defensive, they will keep attacking you. It’s best to push them and make them defend, rather than being pressured. You don’t have to play like this though. Play whatever suits you best.
And up taunt is the best taunt. If your opponent teabags you, kill them and teabag the heck out of them. Maybe an up taunt or two.