Guild Wars 2

The giant destroyer troll at the end of the Zuhl jumping puzzle in Timberline started the fight with a buff that made him invincible (I think it was called “Determined”), and even though we moved him through the lava fonts, nothing would remove it.

“There is a chance that the Giant Destroyer Troll will spawn at The Iron Veil frozen lake. If this occurs, there is no way to kill it because it will be permanently invulnerable. If this happens, let the troll reset and it will be killable again.”

-From the wiki.

http://wiki.guildwars2.com/wiki/Defeat_the_giant_Destroyer_troll