Echoes of Creation: Origin · published
An elite was carrying two and a half times the attack power and double the swing rate of the monster it was copied from. At low levels that was fine. Above level 36, where base attack is already in the thousands, it meant an elite hit roughly seven times as hard as the ordinary version of the same monster — and armour could not touch the difference.
Your client was guessing at monster health between updates from the server, and guessing badly — it counted swings that had actually missed, and subtracted the same hit twice. The bar drifted below the real value during a fight and then snapped back up, which read as the monster healing. It never was. Your damage always counted.
The bar now follows the server exactly. What you see is what the monster has left.
— Tipreth