While I was aware of the Inverse Ninja Law reducing the base HP of Akali / Kennen / Shen when present on the same team, I have recently discovered that they are not the only such champions to have a "Secret Passive".
Nidalee, Cougar that she is, grants younger men lower level champions 5 bonus XP when she levels up. Source
In addition, scuttlebutt says that Leona has a hidden passive as well.
Can anyone spill the beans ?
Best Answer
Sunlight: Leona's passive Sunlight deals one less damage to champion skins wearing sunglasses (eg. Surfer Singed and the Commando skins).
Source: http://leagueoflegends.wikia.com/wiki/Hidden_passive
Here is a link to the LOL files, where the information of the wiki comes.
Another source, is a video of Rift Myths:
NOTE: There is a bug in Jarvan's Commando skin and he do not receive less damage.