One thing that's bad about having a lot going on in a level is that heroes are difficult to manage all the time. They can have a lot happen to them when you're not looking, and when there's a ton of enemies nearby it can be hard to see them. Therefore, when the hero has some type of affliction, there could be an icon next to their Hero Icon to show what they've been afflicted with.
Poisoned: Green Skull
Stunned/Trapped: A Lock
Blocking an Enemy: A Shield
Regenerating (Circle of Life or any healing skill, but not from idle healing): A Green Plus Sign
Under 25% HP: A Red Skull and Crossbones
These icons can be small so that they don't take up too much space and block out important things from the player, but vibrant so they can still be seen and alert the player of their hero's status.