2016-07-13 : Eternal Scourge’s triggered ability only triggers while it’s on the battlefield. For example, Convolute cast targeting Eternal Scourge won’t cause its ability to trigger.

2016-07-13 : You must follow the normal timing permissions and restrictions and pay its cost to cast Eternal Scourge from exile.

2016-07-13 : You’ll exile Eternal Scourge even if the spell or ability that targets it is countered.