Last Legacy functions as an RPG platformer. Due to having an RPGish nature, I think it would be a nice addition to add generic RPG elements.
1.) Leveling System: I think this is self explanatory. Each defeated enemy will grant the player a set amount of EXP. When enough EXP is accumulated, the player will level up and be given points to upgrade his/her stats. The stats could include:
Strength (Physical Damage)
Wisdom (Magic and Ranged Damage)
Vitality (Total Health)
Energy (Total Magic (Meter))
Dexterity (Speed and Jump Height)
Because this game is also a platformer, and given the fact there are no set classes, stat points must be able to be reallocated, whether it be by NPC or a certain item. There must, however, be a cost to reallocating stat points. Having a price would improve total play time and would prevent the player from spamming class build switches. I would also recommend a softcap for the stats. Exceeding the softcap increases the amount of points needed to raise the stat. This will prevent the player from becoming too powerful too soon.
This is all I can think of at the moment. If I think of something else I'll post it here.