Sudden Substitution

• WWizards of the Coast2019-08-23
  Official Ruling
  If the target spell or the target creature is an illegal target as Sudden Substitution resolves, the exchange won't happen. If both targets are legal but are both controlled by the same player, the exchange won't happen.
• WWizards of the Coast2019-08-23
  Official Ruling
  If a permanent spell is exchanged this way, its new controller will control the permanent it becomes.
• WWizards of the Coast2019-08-23
  Official Ruling
  A mana ability is an ability that produces mana, not an ability that costs mana.
• WWizards of the Coast2019-08-23
  Official Ruling
  In a multiplayer game, if the controller of one of the objects leaves the game after Sudden Substitution resolves, the effect that gave them control of the spell or permanent expires. If the spell is still on the stack, the player who gains control of it this way can't choose new targets for it.
• WWizards of the Coast2019-08-23
  Official Ruling
  If the exchange doesn't happen but the spell is still a legal target, its controller may choose new targets for it.
• WWizards of the Coast2019-08-23
  Official Ruling
  The exchange lasts indefinitely. It doesn't expire for the spell if the creature changes zones or leaves the game, or vice versa.
• WWizards of the Coast2019-08-23
  Official Ruling
  The noncreature spell is still on the stack after exchanging control, and the creature is still on the battlefield.
• WWizards of the Coast2021-03-19
  Official Ruling
  After a spell with split second resolves (or otherwise leaves the stack), players may again cast spells and activate abilities before the next object on the stack resolves.
• WWizards of the Coast2021-03-19
  Official Ruling
  Players still get priority while a card with split second is on the stack; their options are just limited to mana abilities and certain special actions.
• WWizards of the Coast2021-03-19
  Official Ruling
  Split second doesn't stop triggered abilities from triggering, such as that of Chalice of the Void. If one does, its controller puts it on the stack and chooses targets for it, if any. Those abilities will resolve as normal.
• WWizards of the Coast2021-03-19
  Official Ruling
  Players may turn face-down creatures face up while a spell with split second is on the stack.
• WWizards of the Coast2021-03-19
  Official Ruling
  If the resolution of a triggered ability involves casting a spell, that spell can't be cast if a spell with split second is on the stack.
• WWizards of the Coast2021-03-19
  Official Ruling
  Casting a spell with split second won't affect spells and abilities that are already on the stack.

Rulings via Scryfall