Had a thought this morn... What if the final skill is something like "Combine" which allowed each class to combine 2 (or 3) other skills into one mega skill. Increased ranks improve any multiplier effects, maybe improve cools down and mana reqs. Works like this...

Learn skill, map skill to screen...

1. Press "combine", and before this skill cools down...
2. Secect up to 2 other skills (also costs selected skill mana and cool down for these start also)
3. The combined skills execute with fantasicly wonderful results - imagine the possible combos!
4. Combine can be cast again, but only with skills not in cooldown mode

As an alternate, for increased specialization, players can only preselect skills to combine when the skill is ranked.. Making it a more fixed but specialized skill.

Click Thanks if u like!