Portal Mage (C17) from Commander 2017, available at 401 Games Canada.

• Rarity: Rare
• Finish: Normal
• Artist: Yongjae Choi
• Card Text:
  Flash
  When Portal Mage enters the battlefield during the declare attackers step, you may reselect which player or planeswalker target attacking creature is attacking. (It can't attack its controller or its controller's planeswalkers.)