Mizzium Meddler

• WOTC Official Reminder Textofficial rules
  Flash — You may cast this spell any time you could cast an instant.

• WWizards of the Coast2015-06-22
  Official Ruling
  If Mizzium Meddler leaves the battlefield before its ability resolves, the targets remain unchanged.
• WWizards of the Coast2015-06-22
  Official Ruling
  Mizzium Meddler’s triggered ability can target a spell or ability even if Mizzium Meddler wouldn’t be a legal target for that spell or ability. However, the target of that spell or ability will remain unchanged.
• WWizards of the Coast2015-06-22
  Official Ruling
  If changing one target of a spell or ability to Mizzium Meddler would make other targets of that spell or ability illegal, the targets remain unchanged.
• WWizards of the Coast2015-06-22
  Official Ruling
  The target of the spell or ability won’t change unless Mizzium Meddler fulfills all the targeting criteria. If a spell or ability has multiple targets, such as Send to Sleep, you can change only one of the targets to Mizzium Meddler.
• WWizards of the Coast2015-06-22
  Official Ruling
  If Mizzium Meddler’s triggered ability targets a spell or ability with no targets, nothing happens.
• WWizards of the Coast2015-06-22
  Official Ruling
  If the spell or ability has multiple instances of the word “target,” you choose which target you’re changing to Mizzium Meddler as Mizium Meddler’s ability resolves.
• WWizards of the Coast2015-06-22
  Official Ruling
  If a spell or ability has a variable number of targets, you can’t change the number of targets.

Rulings via Scryfall