A new idea about awesome support passive

I thought about a support passive: just similar with leona passive but it is randomly cast a mark on a nearby enemy in 5s (like ). That means *Randomly mark an enemy champion with a mark for 3 seconds. When allied Champions deal damage to the target, they consume the mark to deal additional magic damage. * IS IT a good idea? Check out my other idea: http://community.na.leagueoflegends.com/c/ideas/2Ltl3fUA-a-new-idea-about-awesome-support-skill