Vel'koz

When playing with or against a vel'koz, all the stacks of his passive are invisible to everyone except him and his victim with the stacks. As you can see in the gif I posted, the stacks are not shown on the the bot shen or the minions, however it does show an animation when the true damage activates.

To replicate: Play with or against a vel'koz and see if you can see his stacks on enemies or allies.