PSA: Adaptive Helm counters on-hit marksmen's effects.
Champions like Corki, Kog'Maw and Varus who's abilities alter their damage on-hit are countered by Adaptive Helm, because:
"reduces damage from the same damaging spell or effect within 4 seconds."
Just a fun little tidbit for anyone who is frustrated by on-hit and didn't know of this way to counter it.
etc