Garen's Ultimate

I've been playing a ton of games as Garen and against Garen after his rework and have decided he needs a little balancing. His regular passive tends to be a little too strong late game, but that and most of his kit don't bother me. They make Garen Garen. His ultimate is the only thing i have a problem with. The damage is currently quite strong,especially later on, but this isn't what I find to be a problem. It's the passive. I personally love the whole villain idea, but not the true damage that comes with it. It changes the ult damage to true damage and makes his E and basic attacks do true damage as well. But the real problem in my opinion comes from how quickly the mark changes. He can decimate your entire team almost by himself because as soon as the current villain dies, the mark changes to someone else, giving him a lot of power in teamfights. In my opinion, the true damage needs to be turned down just a little bit, but really the mark needs a cooldown before it changes to someone else. Tell me what you think.