Blightcaster

• WWizards of the Coast2013-07-01
  Official Ruling
  Blightcaster's ability will resolve before the enchantment spell that caused it to trigger.
• WWizards of the Coast2013-07-01
  Official Ruling
  If you are the only player who controls a creature when Blightcaster's ability triggers, you must choose one as the target, although you can choose not to give it -2/-2.
• WWizards of the Coast2015-06-22
  Official Ruling
  If you are the only player who controls a creature when Blightcaster's ability triggers, you must choose one of those creatures as the target, although you can choose to not give it -2/-2.
• WWizards of the Coast2015-06-22
  Official Ruling
  Blightcaster's ability will resolve before the enchantment spell that caused it to trigger.

Rulings via Scryfall