Izzet Chemister

• WWizards of the Coast2018-03-16
  Official Ruling
  You must cast any of the exiled cards you wish to cast while Izzet Chemister's last ability is resolving. You can't cast them later in the turn. A sorcery cast this way will be cast at a time you normally wouldn't be able to.
• WWizards of the Coast2018-03-16
  Official Ruling
  If you cast a card "without paying its mana cost," you can't pay any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, such as that of Tormenting Voice, those must be paid to cast the card.
• WWizards of the Coast2018-03-16
  Official Ruling
  Any of the cards you don't cast will remain exiled.
• WWizards of the Coast2018-03-16
  Official Ruling
  If the card has in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
• WWizards of the Coast2018-03-16
  Official Ruling
  The last ability of Izzet Chemister only lets you cast cards exiled by that card. If Izzet Chemister leaves the battlefield before you activate that ability, the exiled cards are lost forever.
• WWizards of the Coast2018-03-16
  Official Ruling
  You cast the exiled cards one at a time in any order. Later spells can target ones you cast earlier. None of the spells resolve until after you're done casting them all.

Rulings via Scryfall