New Devourer question

yes

Just did it with Kayle.. seemed to be working..

It works, Runaan's applies all on-hit effects to all three targets, including it's own on-hit effect (extra 10 damage turns to 20 every second attack on all your targets).

This is especially good on champions like Kog'Maw, who take advantage of it heavily (His W does HP% damage on-hit to all three targets).