it doesnt matter if Lucas in Brawl would spoil Mother 3 events, just look at Sheik in Melee.
Also, why dont Lucas has the PK and PSI attacks that Ness didnt get in Melee:
Ness:
B=PK Flash
>B=PK Fire
^B=PK Thunder
Down B=PSI Magnet
Final Smash=PK Rockin (Ness-only tech, big psychic-like attack that damages all enemies)
PK Rockin
http://www.youtube.com/watch?v=lsh37VUfa7Y (1:58)
It could cast colored beams from left to right and then right to left, cousingdamage and getting enemies closer to Ness, the he would cast a final powerful psychic wave that sends enemies flying. The final wave doesn't have that much range to the beams, which is the point of bringing enemies closer.
Lucas:
His specials can be based on this attacks:
PK Love (lucas version of Ness's PK Rockin)
PK Freeze (ice-based attack that can sometimes freeze enemies and it is known for the low use of PP (like energy...TP) compared to the its power (low PP for high damage)
PK Ground (does 5 unmissible ground-based attacks (except for flying enemies, that can sometimes miss))
PK Starstorm (Kumatoras similar vercion of Lucas's PK Love, its a little bit weaker to PK Love max version)
Refresh (Lucas-only tech, it heals small amounts of damage every turn for a period of time)
Sheild (reduces physical damage 3 times)
Psycho-Sheild (redusces PSI damage 3 times)
Sheild-Counter (same as Psycho-Sheild but it also returns damage at enemies)
Paralysis (paralizes enemies)
Hipnosis (puts enemies to sleep)
Brainshock (confuses enemies, making them attack their allies or themselves sometimes)
PK Starstorm and PK Love
http://www.youtube.com/watch?v=x6ahPxGYKrQ (1:15 and 1:20)
This attacks doesn't have to be similar in some way to how they originally are in the Mother games, like PK Fire, in the game it damages all enemies, while in Melee it only damaged one character unless other characters where really near to it. PK Flash coused different status effects or instant defeat sometimes, the instant defeat was the only thing that can be related in some way to the Melee PK Flash, because of the high damagedone by it. PSI Magnet absoved PP (energy or TP), in Melee, it sheilded you from missile attacks, and in this case, it healed you. PK Thunder summoned 1 to 4 lightning that could damage or miss the target randomly, in Melee, it is only one lightning , it's ball-shaped, you control the direction and can be used for recovery.
But they should have something similar oviously, like PK Fire is fire based, PK Flash can sometimes instant-kill you, PK Thunder is lightning-basd and can sometimes miss if you don't master it and PSI Magnet absorves damage.
So...this is my Lucas:
B=PK Freeze - casts a ice-like wave around Lucas, it hits ones, it can sometimes freeze the foe, it can be charged for bigger range and damage. It it is a quick attack(in reference to the low PP consumation) with decent damage.
>B=Sheild-Counter - creates a energy-psychic sheild in front of him and shots it forwards, increasing the sheild's size. Imagine Invisible Woman's sheild that she does in the first Fantrastic Four movie to Doctor Doom in the office scene thing. It has small/mid range, is not that powerful, it pushes enemies away and it reflects missile attacks (in reference to it sheilding and reflective abilities it had in the game). It kinda leaves you open from behind.
^B=PK Starstorm - Stars would star appearing below him, shooting them upwards in a spreaded fashion, blasing himself up. The stars can hurt enemies and if you do this with a enemies sticked to your side, all the stars would eventually connect with the enemie, cousing a big amount of damage (in reference to the big amount of damage it could couse in Mother 3). It leaves you kinda open at the begining of the attack.
Down B=PK Ground - It casts a wave on the ground that does small/mid damage and can be done 5 times in a row. It knocks foes back a little, but the waves eventally get bigger (the first wave is small, but the 5 is kinda big) so all the waves connect most of the time.
Final Smash=PK Love - Something different to PK Rocking I guess, like casting powerful psychic explosions in random places of the stage.