Garen's W "Courage" reduces incoming true damage.

Garen's W works differently than any other damage reduction ability in League. Alistar, Maokai, Braum, and Katarina all take the full amount of true damage when their damage reduction abilities are active, but Garen's W active for some reason Reduces true damage, so I'm pretty sure this wasn't intended.

I was laning against a Garen as Irelia, and upon gaining max rank of W (which should do 75 true damage every auto), if Garen activated his W he would only take 42 true damage per auto.

This also works against Gangplank passive.

You can reproduce this 100% of the time by playing any champion that does (preferably flat, easier to notice) true damage, and activating Garen's W.