One of Lucas's alternate costumes has him with brownish hair, right? Well that's supposed to look like Lucas's twin brother, Claus.
Lucas's aerial back attack is a Meteor Smash if used at the right time.
His PK Thunder can go on after attacking one person.
He enters on a Mr. Saturn Tea Table, which was a transportation vehicle in Mother 3.
One of his victory taunts shows him pulling something up. That "something" is one of the Needles from Mother 3, that, once pulled, a Dark Dragon is released from, and it's mentality (Good or evil) depends on the heart of whoever pulled it.
The reason his PK Fire attack with an aftershot, but Ness's stays in place, is because in Mother 3, PK Fire attacks all enemies. In Earthbound, PSI Fire (Yes, it's called PSI Fire instead of PK Fire) attacks only one row of enemies, so it would of course not attack any farther.