Will Split trigger Prodigy for each Magic Missile fired?
After some testing it does appear that multiple hits by using the 'Split' rune will trigger multiple effects from the 'Prodigy' passive ability. With this in mind in conjunction with the thread you've linked for Electrocute, I believe it safe to state that the 'Prodigy' passive will proc every single time one of the signature abilities hits. This should mean that the 'Spectral Blades' ability is overpowered for Arcane Power regeneration.
After some further testing with Spectral Blades I can confirm this is actually how the 'Prodigy' passive works (one attack with Spectral Blades on a group of 7 enemies resulted in my Arcane Power going from 'nearly empty' to 'nearly full' in one attack).
My methodology for testing:
- Act 1 inferno, first quest
- Arcane Orb as my secondary attack
- Prodigy active as one of my passives
- Magic Missiles + Split rune as my primary attack in the first pass
- Run out past Rumford at the gate into Old Tristram Road, you'll meet a pack of 6-8 mobs
- Empty Arcane Power using Arcane Orb
- Attack the group
- Observe results
What I found:
- Magic Missiles without the Split rune will provide less Arcane Power than with the Split rune
- Spectral Blades on a large group will provide Arcane Power back for every enemy that is hit
- Electrocute will provide Arcane Power for targets hit by the chained element of the attack
Conclusion:
The 'Prodigy' passive ability does exactly what it says it does. When you deal damage with a Signature ability with the 'Prodigy' passive enabled, you will get 4 Arcane Power per enemy that is damaged during that cast.
This stacks with the equivalent runes on the abilities themselves, so you can use Prodigy + Siphoning Blades, for example.