A while ago a rioter said that Navori would not increase spells such as Kog'Maw w or other on hit effects.
After testing this item out on live servers however, it does increase kog w dmg as well as vayne w, and multiple adc passives such as twitch and kaisa. I am not sure if this is intentional, and if it is please keep it in the game, as it results in a much larger base of champs being able to purchase this item. The one thing that I did discover while testing is that it also increases the limit of dmg an ability can do to monsters. Kai'sa passive has a 400 dmg limit to monsters, but with navori this can be increased to ~480, same with Kog, and varus blight stacks.
Not sure if any of this is intended, but just wanted to let people know that Navori will be worth getting on more champions than initially thought.