^ Interesting thoughts on staying with the more comical Super Smash Bros. 64... but with the way the gaming public is today, if it's too lighthearted, people will bash it to "kiddy" hell. (Ah, and you don't have to worry about posting characters and whatnot in the fashion I do... Heh.)
As for Mewtwo... I don't understand why he was cut in the first place, either. However, I cannot say with a straight face that I would want Lucario to be replaced, either. He's become my most longest played character (surprisingly), and is the ONLY character in the Smash series to do the more-percent-more-power bit. That's unique, which makes him pretty cool. Other than that...

SKINS
CHALLENGER APPROACHING! BATTLE THEMEVersus Legendary! - Pokemon Diamond/Pearl/Platinum
Alt.:
Versus Primal Dialga - Pokemon Mystery Dungeon: Explorers of Time/Darkness
MOVESIntro (when he appears on the field): A black spot/void appears on the ground, and Darkrai slowly emerges head-first.
A: Swipes at foe weakly
A: Swipes foe again, with a little more force
Smash Attack>: Darkrai lashes out with dark energy at his fingertips. Tip of fingertips has most power/knockback.
Smash Attack^: Darkrai uses both hands to create a ball of dark energy above his head that shoots into the sky a short range. (Dark energy ball still causes minor damage as it's loading in his hands.)
Smash Attack v: Darkrai raises his arms, then sharply drops them so that they're parallel with the ground. He releases some of his red aura as he does this. This move works similarly to Lucario's down Smash Attack.
Crouch: Darkrai's body sinks into the ground. Only his head is visible. If one were to see what he looked like from above, they'd see his flowing "hair", his head, and what appears to be his body in the stage as a shadow.
Crawl: Darkrai's body, hidden in darkness, slowly creeps forward or backwards.
Strong Attack>: Darkrai lashes outwards with this hands.
Strong Attack^: Darkrai uses a hand to swipe away enemies with a dark force.
Strong Attack v: (While crouched) Darkrai slightly shoves enemies away with telekenetic powers.
Rushing Attack: Darkrai shoves away his opponents with a red aura pulse.
Neutral Special Attack: DARK PULSE - Hold the B button down for more power; move will automatically release once charged completely (think Marth and Ike's B moves); the longer held, the more damage done and farther range. Dark energy pulses from Darkrai's body.
Special Attack>: SHADOW CLAW - Can be used twice in a row; Darkrai swipes downwards at the enemy first swipe, then upwards the second. He uses a ghastly energy...
Special Attack^: PURSUIT - Darkrai automatically locks on to the closest opponent and hits them. Depending on if the enemy is idle or moving, the attack's power weakens or intensifies respectfully.
Special Attack v: HYPNOSIS - Darkrai lulls nearby opponents to sleep, giving them minor damage as they doze off. Their length of sleep depends on how much percent they have accumulated, and the distance away they were from Darkrai when he executed the attack. Cannot lull enemies to sleep in the air.
Grab: Grabs with both hands.
Grab Attack: Sends dark energy coursing through the enemy.
Throw>: Darkrai suspends the enemy slightly in front of him, holds a hand out, and shoves them away telekenetically.
Throw<: Darkrai throws his enemy over his shoulder as dark energy clings to their body.
Throw^: Darkrai suspends the enemy above him for a moment, then shoves them into the sky via telekenetic powers.
Throw v: Darkrai envelopes the enemy with dark energy as they bounce off the ground beneath him.
Neutral Aerial Attack: Darkrai pulses with red aura. Has decent knockback.
Aerial Attack>: Darkrai slashes at the air in front of him with dark energies.
Aerial Attack<: Darkrai (with legs extended) kicks backwards twice. The tip of his legs has the most knockback power.
Aerial Attack^: Darkrai uses dark energy to create a small explosion above him (similar to Zelda's Aerial Attack^ .)
Aerial Attack v: Darkrai brings down his hands to create a small burst of red energy. *Meteor Smash.*
Taunt^: Darkrai's body is outlined in red aura and he grunts, amused.
Taunt>: Darkrai clenches a hand into a fist, which exerts dark energy. He shudders, grunting.
Taunt v: Darkrai sinks into the shadows and reemerges quickly; "Huh, huh..." he chuckles.
Special Effect(s): Darkrai hovers slightly above the ground, and does not trigger items such as Motion Sensors or Snake's mines due to levitation.
Final Smash: DARK VOID - Darkrai breaks open the Smash Ball... He executes Dark Void by putting his hands above his head. A black ball of energy appears in his hands, then swiftly expands, engulfing anyone nearby. Anyone in the viscinity of Dark Void is put to sleep, and their percentage slowly rises. Enemies that are in the air, but end up inside the void, fall to the ground unable to recover unless they escape the void. (Think Luigi's Negative Zone.)
Winning pose 1: Darkrai glides in from the shadows and emerges, body flowing.
Winning pose 2: He clenches his fists, eyes closed, and a red aura exerts from his body. He then opens his eyes and chuckles.
Winning pose 3: Darkrai, his back partially to the camera, peeks to the side to view the player. His eye flashes red, and his body flows.
~~~~~~~~~~~~~~~~~
Now that I think of it... There's one certain option I've been looking forward to in the Smash games: the option to colorize your character. As in, you could have a pink Sonic fighting a gray Charizard, or a Midna-inspired Zelda fighting a Shadow Queen-inspired Peach! Personally, I think it would be awesome to color in your characters... Sure, then there'd be no point in optional colors to come with the characters, but hey, it's always nice to have your customs displayed with the professional choices.