Every Champion's Passive is a second trinket item you can buy

Okay, for the sake of the thread, riot adds a second trinket slot and just for that slot you can buy another champ's passive ability to add to your own. What are the most OP combos, most UP combos, most frustrating, and the most interesting/exploitable combos?

Most op - Katarina getting Annie's passive (stun death blossom). Ashe getting Yasuo's would be a second to that. Most up - Soraka gets Janna's prenerfed passive and low allies kite you even harder. Most Frustrating - Aatrox or Anivia getting each other's passive and then buying a GA. Most Interesting - for me that would be adding eve's passive to Ahri.