Idea to regen mana in patch 6.9

Buy on midlaners. Challenging helps quite a bit in duels with the % damage reduction, and the low cost of runic echoes makes it very good early.

Even better than that is that if you are running low on mana, you can chuck a low cost spell into your wraith camp to restore 18% your missing mana, which seems like it is going to be the best way to regen mana short of recalling in that patch.