Runaan's Hurricane effects for these champions
Abilities that only apply to the projectile fired at the primary target:
- Spinning Axe
- Transform: Mercury Cannon
- Righteous Fury
- Silver Bolts
- Pix
- Clockwork Windup
Abilities that affect the primary and secondary targets:
- Hyper Charge
- Fishbones
- Electric Surge (Mark of the Storm proc only, not the bonus damage)
Rule of thumb for Runaan's bolts applying something: If it's "on next hit", or can only generate stacks on one unit at a time (Sheen, Silver Bolts, Clockwork Windup; but not Mark of the Storm) it only applies to the main target. If it's on every autoattack, it probably will apply to all targets hit.
Lots more interactions listed here: http://leagueoflegends.wikia.com/wiki/Runaan%27s_Hurricane