I'm surprised that people think Pikachu isn't at least top 3. He's way faster than every character but Sheik and has an Up smash that's almost as good as Fox's.
When Pikachu stops being able to combo a character from a throw Pikachu can use a thunder jolt to easily pressure the character into a punish. Thunder Jolt seems as useful as Luigi's fireball but Luigi's might be a little better.
Luigi's fireballs are absolutely insane.
-Get hit/shield fireball >> get grabbed comboed into 50%
-Get hit/shield 2nd fireball >> get grabbed add another 20%
-Get hit/shield 3rd fireball >> get grabbed add another 15%
-Get hit/shield 4th fireball >> get grabbed get killed by tornado, b-air, b-throw
Obviously exaggerated but pretty much Luigi kills you with four fireballs.
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And Pikachu does not rack up damage IMO. His damage output is fairly low in a balanced manner.
I think Ness and Luigi damage output is absolutely insane and a bit questionable. They hit as hard if not HARDER than heavy hitters! For example here are some data for your convenience judge for yourself:
(consider the priority and how fast Ness/Luigi aerials and how little cooldown it has)
Ness:
N-air 7%,
11% (clean)
F-air 7%
B-air 8%,
15% (clean)
U-air
13%
D-air 10%,12%
Luigi:
N-air
12% (why..?)
F-air 9%
B-air 14%
U-air 11%
D-air 10%
Ike:
N-air 9% (clean), 6% (late)
F-air 12%
B-air 14%
U-air 11%
D-air 15%
Charizard:
N-air 10% (flame), 7% (tail)
F-air 11% (early, clean arm), 12% (clean tip)
B-air 10% (body), 13% (tail), 15% (flame)
U-air 13%
D-air 14% (clean), 8% (late)
Donkey Kong
N-air 11% (clean), 8% (late)
F-air 16%, 15% (sweetspot), 13% (sourspot)
B-air 13% (clean), 8% (late)
U-air 13%
D-air 16% (sweetspot) 13% (sourspot)
Marth
N-air 2%/3% (hit 1), 6%/8% (hit 2)
F-air 7%/10%
B-air 9%/12%
U-air 9%/12%
D-air 11% (blade), 13% (non-meteor tip), 14% (meteor tip)