Pantheon and Mordekaiser switch places for a day
They keep their original passives, but they switch their abilities.
http://i.imgur.com/agH64Ci.jpg Pankaiser: The Iron Artisan P: Aegis Protection Q: Spear of Spades W: Harvesters of Zeonia E: Siphon of Heartseeker R: Children of the Skyfall
http://i.imgur.com/CUqQmmR.jpg Mordetheon: The Revenant of War P: Iron Man Q: Mace Throw W: Aegis of Sorrow E: Strike of Destruction R: Grand Grave
Tl;dr Pantheon loses his mobility and poke for short range domination while Morde loses his dueling potential and 6v4 for gets more mobility and poke.