I think the runes are going to be a learnable language in RiftRunner rather than a magic system. Magic will probably come under the realm of skills, same as Divine Divinity.
I do like the idea of combinable rune magic though. It could be similar to the magic-card system in Septerra Core. Each player could hold one card and a lead character would cast the spell. You could combine cards to produce different effects (with higher energy consumption) such as inversing the effects (Slow + Mirror + All = All allies act faster).
In RiftRunner there could be a Rune Magic skill. Level 1 lets you use runes and each level after that lets you combine more runes (5 runes at level 5). By combining runes, their powers magnify each other and runes can be combined in advance using drag-and-drop. You could have a rune menu, like the potion menu, to quicky cast them. Each extra rune provides a higher effect. Two runes magnify all effects by 1.5, three by 2, four by 2.5, and five by 3. So:
Curse + Lightning + Fire + Fire = Curse (2.5) + Lighning Damage (2.5) + Fire Damage (5)
Heal + Heal + Heal + Heal + Heal = Restoration (15)
So higher levels of skills, which cannot be learned, can be achieved by using runes.
Would runes use mana? Perhaps not because you have to find the runes before you can use them. They'd be more common than charms, though.
