"Forward" is the direction your character is facing, not where the camera is facing, if that helps.
walking up isn't part of any input or special attack for most characters
luigi is just a better version of mario tbh
luigi's super 1 and mario super 1 is big difference
lets say u have bad aim / not hitting the mario super 1
you can hit others a lot easier, and also more range
also luigi's uppercut is better cuz it is more higher ( so they stay up in the sky longest )
and super 2 the same just time difference