The idea is as follows -

• Everyone gains an ability that costs AP that gives them a source point (1 turn cooldown) and a debuff that lowers AP per turn to Zero but makes this skill also cost zero
  
• All Source skills cost 0 ap
  
• When the player moves/moved or casts a source ability, they lose the debuff.

The idea being to change source to an in combat mechanic where you have to take several turns to cast big powerful spells. So you can cast something like a 3 source point meteor whenever you want but you'll have to take 4 turns total to execute it (3 charging source then the 4th casting).