Just about everyone in the show has been used for this song at some point in the past, so filling this role came down to who fit the part best. And I am ashamed to say that I couldn't decide. But you can! I've made both videos and posted them together. Pick which one fits Scar better and that one will become the official video.

Edit: Luna has won the part! Thanks for your opinions!

In favor of Discord: My Celestia, that voice! This song just sound right coming from Discord. And he's definitely got the facial expressions to pull it off. One of the evilest beings in existence for one of the baddest villains of Disney.
Against Discord: He makes no sense from a casting role. I know I've held loose species before, but Scar is supposed to be Simba's family. In that regard I'm stretching it already using an alicorn in the other video, but this is almost absurd. But can you all overlook that? If you can, than Discord it will be!

I do not own My Little Pony or Disney, but that's not important right now. WONDER FILLIES POWERS ACTIVATE! Shape of a shark! Quick, Diamond Tiara, jump into my jaws!