Character Progression System (aka leveling up, learning new abilities as you level up, etc)
That's very easy, just set up an instance variable called "Level", and an event for when you level up.
Battle System (most likely a twist on the above menu system) (battle menu system to use specific abilities in a turn based format against enemies. Include enemies AI as far as attacking your characters. Perhaps some specific method of attack for boss enemies that is a little harder, and also include specific cool abilities for more rare enemies.
Once you understand the basics of combat mechanism, the rest of this is fillers.
Trouble is, nobody seems to want to say how the basics of combat works, either turn based, or melee; no tutorials, nor simple capx. This basic unhelpfulness is a bit frustrating.