I like the idea, but I feel like the passive might be unnecessarily restrictive and unnecessarily broad at the same time. This sounds like a paradox, but I have a good reason for it.
First off, refunding 10% of the mana being used for an ability actually might be too small to actually be useful. For example, Malzahar's E costs 120 mana at rank 5, and this passive will restore 12 mana when Malzahar uses his E on a jungle monster, and that isn't good enough sustain to get through the jungle. This kind of passive would favor champions who have low-cost damage spells that they could spam really fast and hurts champions that have dedicated utility spells they need for sustain in the jungle or have toggled abilities they need to clear the jungle. Obviously values can be increased if they are too weak, but this iteration doesn't seem to be too universally favorable.
Next, energy or health costs don't have the same problem that mana does. The problem mana does is that it limits you to either farming your jungle or ganking a lane when you don't have a big mana sustain item, but energy doesn't do that because it regenerates so quickly and health doesn't matter because it's usually compensated by some form of sustain in the jungle that really starts to kick in around the same time you buy Magus.
Finally, adding a bleed effect on monsters is somewhat unnecessary because AP champions can clear fine by the time they get their jungle item. The bleed effect probably isn't necessary because all AP champions need is mana sustain to clear the jungle because their kit already clears the jungle well.
Personally, I think that for all of Runeglaive's weaknesses, I think that the mana regeneration portion of its passive specifically was rather well done. It gives sufficient mana regeneration for the jungle distributed on a need-by-need basis without being abusable in lane. However, it does have some restrictions and some abuse cases, and I feel like Runeglaive's mana regen portion can be salvaged into something more universally usable.
My iteration:
Magus: builds out of Fiendish Codex + jungle item + gold
80 AP
10% Cooldown Reduction
UNIQUE Passive: Spending mana grants a buff that stacks up to three times. Dealing spell damage or killing a monster consumes all stacks and restores 8% of your missing mana for each stack consumed. The first stack cannot be consumed until 1 second after it is obtained or until after a second stack is obtained. Stacks do not fall off until being out of combat with neutral monsters for 6 seconds
Basically, this iteration has many of the strengths Runeglaive has without many of its weaknesses. In particular, it has pretty solid stats and has a more universally useful passive, of which is more useful on champions that rely on toggled abilities (due to proccing on mana expenditure) or champions that want to combo their abilities much more tightly than Runeglaive's current passive allows (due to a stacking system and no cooldown on the passive), and it's not abusable by mid laners because it's not usable on lane minions and most champions can't apply it on a single spell cast. Champions with manaless spells that use mana also can't abuse this passive to gain massive amounts of mana because it only applies on mana expenditure, rather than spell usage. Best of all, those that really need it get all the mana regen they need while those that need it less don't get as much from it.