2019-08-23 : A mana ability is an ability that produces mana, not an ability that costs mana.

2019-08-23 : If a permanent spell is exchanged this way, its new controller will control the permanent it becomes.

2019-08-23 : If the exchange doesn’t happen but the spell is still a legal target, its controller may choose new targets for it.

2019-08-23 : 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.

2019-08-23 : 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.

2019-08-23 : The exchange lasts indefinitely. It doesn’t expire if the spell or the creature changes zones or leaves the game.

2019-08-23 : The noncreature spell is still on the stack after exchanging control, and the creature is still on the battlefield.

2019-08-23 : While a spell with split second is on the stack, players can take special actions such as turning a face-down permanent face up.