How do I get better with Ness and or Pikachu?
Hmm. I'm not too good with either of those two, but I'll give you some tips I've seen other folks give!
Ness: F-Smash reflects projectiles at double their original speed. Take advantage of it! Hitting yourself with PK Thunder causes a long ranged tackle. This move, known as PK Thunder2 is a risky, but satisfying KO move. Just watch your aim; there's no recovering if you fly off the stage! PK Fire is great for damage racking, but watch for reflectors! PK Flash is powerful, but slow. Release B just before it hits the floor for maximum power! Finally, PK Magnet absorbs projectiles, but ONLY energy-based ones. For example, Fox/Falco's lasers, Samus's charge shot, etc.
Pikachu: Take advantage of your speed and small size to avoid danger! Thunder Jolt is a useful projectile, but requires floor space to be effective. It can crawl up any wall for a limited distance! Skull Bash is a handy charged attack. It's also good for horizontal recovery! Quick Attack doesn't deal much knockback, but its range makes it good for recovery or chasing foes! Finally, Thunder deals extra damage if it hits Pikachu himself. Also, if you hit an airborne foe with the cloud itself, they'll be spiked downwards!
As i said, I'm not too good with those two, but I hope this helps!