Throwing[edit]
Often regarded as the best throw in the game (or maybe Pikachu), Ness's pyschic toss is extremely powerful, as well as quick. Needless to say, this move should be used extensively by any competent Ness player. Be sure to take advantage of the slight, stunning damage done to other players near Ness during the "wind up" before the throw. Throwing techniques are quite extensive, and are best learned by practice. Another thing to note is that Ness remained invulnerable while he is executing his throw, so in multiplayer games timing a throw after an opponent is grabbed can often avoid an attack from another player.
(The PK fire is a great [and usually unexpected] way to set up a player for a throw.)
Juggling[edit]
Ness's tilt up is the best for juggling, especially at low damage against heavier characters. However, starting this juggle is a bit tricky, since if you tilt up while on the ground you will jump instead. The simplest way to do it is to jump, then attack the enemy with dair, followed immmediately by a tilt up. The idea is to hit them up while they are bouncing off the ground from the dair. Make sure you tilt the analog stick up before you hit the ground, or you will instead jump. A great way to finish the juggle is with a smash up, but must be timed to avoid the invinciblity the enemy has when getting up.
Ness's usmash (quick semi-circle yo-yo) can be effectively employed to juggle opponents when against walls, especially larger, heavier opponents like Donkey Kong. To execute this move, use 
+
.
Ness's spike kick (dair smash) can be incredibly useful for ground-juggling. A dair smash on a character will cause an opponent to bounce. Follow up the dair with a slight jump and another dair as the character is in the air from the bounce. This will cause the opponent to bounce again, a little higher. Compensate for this by jumping a little higher and dair again. As the opponent bounces higher, you can get more than one dair per jump with Ness. A good way to finish off this combo is with either an uair (headbutt smash, though this doesn't always KO) or by jumping just to the side of a bounced opponent and back-kicking them off the side of the map.
The throw can also be effectively used for juggling. You have to throw the player against a or other object, so they bounce off and come back to you. This is excellent on the Great Fox level, where the wall is tilted slightly down. They will always bounce right back to the ground, where you can grab them again right as they hit. As their damage increases, you must adjust your position further away from the wall. This is impossible to escape from if performed correctly.
Edge Play[edit]
One of the most lethal edge moves in the game is Ness's dair. Spiking w/ Ness is quite common, and involves jumping out and smashing the opponent directly down with a dair. To prevent Ness from flying downwards, the dair is ideally performed immediately after the first or second jump, and with minimal tilt of the stick. KO's can be achieved against even 0% opponents, using a quick throw/spike.
In the case of a missed spike, PK thundering yourself directly at the opponent while they are climing back up is a great recovery/attack tactic (just don't hit the wall).
If you realize you have jumped too short / too late, always remember to use fair, or even uair if necessary.
The dsmash is also great for those who are just barely making it back. Because of initial back swing of the yo-yo, timing is important, but it does protect you from those trying to attack you from behind and take your K0.
There are two other edgeguarding strategies that Ness can employ when an opponent is hanging on the edge. One is to execute a very precise dair to smash the fingers of whomover is holding on to the edge, prpelling them quickly to their death. This is very difficult to execute, however, due to the tiny area opponents are holding on to. Ness's dash attack (affectionately called his "Prayer" attack) is also useful for knocking opponents off the edge, propelling them outward and downward. This can often be followed up with a dair (spike kick) for a quick kill.
Usefulness of PK Thunder Against Opponents[edit]
The PK Thunder attack can be very useful in disrupting players' recovery efforts, though it is more effective versus certain players than others. Against most players, the best time to hit an opponent that is trying to recover is before they use their second jump. The PK Thunder takes away the second jump, or, if it hits during the second jump, will make the opponent lose all the momentum of their second jump. Against a third jump, the PK Thunder often just helps opponents recover, as it gives them back their third jump. This is particularly evident against players like Captain Falcon. It is important to remember, though, that Ness is extremely vulnerable while executing his PK Thunder attack, and missing leaves him with a PK Thunder floundering around in the sky while opponents can walk up to him and throw the crap out of him.
When fighting other Ness characters, you can hit their PK Thunder recovery effort with one of your own when they are coming back. They cancel each other, and your Ness opponent will fall helplessly to his death.
Kirby is especially difficult for Ness. It is difficult to bring down an aerial Kirby, because of Ness's slow, loopy jump. If the Kirby is stupid enough to try the brick or bup, a simple roll/throw is quite effective. When floating around, however, Kirby can't use his shield against Ness's PK Thunder projectile. If your opponent insists on flying away constantly, just assault him with PK Thunders until he comes down. The small damage will add up, especially against the light Kirby (or Jigglypuff).
Against Fox, PK Thunder can often disrupt his Jet Pack move and stun him for a long enough time that he won't be able to make it back. This is especially possible if Ness can land multiple PK Thunders throughout Fox's recovery.
Against Donkey Kong, PK Thunder can be effective as well, especially because Donkey Kong doesn't have a very good vertical jump and every fraction of a second spent falling lower can be costly. The PK Thunder will get cancelled out at the beginning of his Spinning Kong, but hitting him about half way through the Spinning Kong will send him almost surely to his death (althought it might take one more PK Thunder).
The PK Thunder attack can also do what is called "tailwhipping" an opponent, that is, come close to the opponent and hit them a little bit but continue on its path. This can occasionally be employed to double-hit an opponent working his way back to the edge of the map, but it is very difficult to do.
Free Health[edit]
Never forget the PSI Magnet (Bdown). While difficult to use against human players (who learn quickly not to fire their energy attacks at you when you can absorb them), it is especially effective against computers (who will fire at you until you're fully healed), and more importantly, certain environment hazards. The Pokémon Starmie, Meowth, Charizard, Charmander and Venosaur have projectile attacks that can be absorbed quite easily. Just jump above the projectile stream and Bdown while falling into it. Don't hit the actual Pokémon, though, as it will still hurt you. The best place to absorb damage is from the Arwing on Corneria. Each shot recovers you 40%, and the ship almost always shoots when you jump if front of it. The best way to absorb Arwing's shots, however, is to stand on the very tip of its nose. It will carry Ness along with it as it charges him up. This method of damage percent recovery is liable to piss off opponents to no end, and has even been called "cheap" on the Great Fox level. The PSI Magnet can also be used to slow Ness's descent, particularly useful on DK's level. When shot far off the stage, using the PSI Magnet, then the second jump, then the third jump, Ness can almost always get to the barrel underneath, even if it is on the far side of the stage when he was knocked off.
Shooting yourself[edit]
Become an expert at shooting yourself accurately. With a little practice, you can snipe entire groups of people with this attack. Be warned, this move has a long down time afterwards, leaving Ness extremely vulnerable. Also, it is easy to see it coming, so it is most effective against groups already engaged with each other. To shoot yourself, use PK Thunder ( 
+ ) and then use 
to direct the PK Thunder and make it touch you.
When shooting yourself back to the edge, special techniques must be used to avoid the downtime after the move. Otherwise, opponents will shield while you shoot yourself, wait for you to land, and throw/smash you back off during the downtime. This is probably one of the more difficult things to deal with in advanced play, and can completely negate the massive recovery abilities of Ness. When falling from above the level, an effective strategy is to try to launch yourself exactly parallel to the ground. Ness will fly along the ground, and when he comes to a stop, he won't experience any downtime. Another tactic is to DI yourself below the edge, and shoot yourself up so that you grab the edge. This allows you to take advantage of the short invincibilty when climbing up. (Note: shooting yourself directly at the edge, without falling below it first, often results in Ness simply "bouncing off". This is incredibly annoying and should be avoided at all cost)
Also, your enemy might figure out that if he jumps out and purposely gets hit by your PK Thunder, then you will die. To avoid this, go around Ness the other way with the PK Thunder if you see him coming. It is possible with a little practice.
Baseball bat[edit]
Ness's bat is quite powerful, and the "homerun" sound is quite satisfying. However, it is rather slow, and is best used only in combination with another stunning attack. Against a low to medium damaged enemy, a dash attack immediately followed by a bat is quite effective. This attack is not as powerful as the baseball item's homerun swing, however, so picking up the item is still useful for Ness besides normal attack and projectiles.
The bat will reflect most projectiles back where they came from. Usually absorbing the attack is better, but it is fun to try your hand at some baseball. A great level to practive on is the Great Fox level with the Arwing. If you are in front of the Arwing, it will usually shoot at you. If you watch the Arwing closely, you will see a green flash right before the lasers come. This helps you time the bat better. Batting the lasers at someone else is an incredible feat, and may cause them to cry.
(Note: A glitch in the game will occur if you bat a PK Thunder that Fox has reflected back at you. The PK Thunder becomes double tailed, and the games freezes as soon as it hits anything.}