This design idea come from Hearth Stone.
Overcharge is a debuff that can be created from attack or abilities, it can stack at most of 5 levels.
Overcharge under 5 level did not has any negative effect, but when the target with 5 levels of Overcharge receive additional Overcharge effect, the target will get 75 damage and Shocked if it is not a hero.
For example, Elemental Shaman's Chain Lightning will add 1 level of Overcharge to each target, at first it seems has no harm but only lightning on the foot. But when more and more units has 5 levels of Overcharge, they will receive 75 damage each time when getting another level of Overcharge, and may be neutralized in short time.
Overcharge are created from attacks of certain unit or abilities. Both Alliance and Horde has units to create Overcharge. And the Thunder King would be a master on creating Overcharge effect.
