A thought on how to keep Sated Devourer from (potentially) breaking the game.

Raise the number of autos required and use a stacking system for the unique passive.

Something along the lines of

"Unique Passive: Phantom Hit - Every basic attack will accumulate 1 stack of "Phantom Hit", upon reaching 4 stacks, your next basic attack will trigger a phantom attack, that triggers all on-hit effects a second time

Stacks fall off when not in combat after 5 seconds."

TL;DR: every 5th auto now procs phantom hit, it works on a stacking system like some other on-hits.

If needed, you could probably hard-code it to make it only work with ACTUAL autos (so Yi or Shyvana can't get multiple stacks in a single auto)