When Stormbringer targets a friendly unit (Sand Wurm) and moves it to an enemy-controlled battlefield (where Kai'Sa is), and the defending player has a hidden Fae card, what is the correct resolution sequence?

Ruling: Stormbringer deals damage to all enemy units at the chosen battlefield, then moves the friendly unit (Sand Wurm) to that battlefield. When the unit moves, contested is applied immediately (before cleanup), which locks control of the battlefield. During the subsequent cleanup, Kai'Sa dies from damage, but the hidden Fae card is NOT discarded because the battlefield remains controlled (contested prevents control change). A combat is then staged, and during the showdown for this combat, the player can play the hidden Fae card.

Sequence:

• Stormbringer resolves: deals damage to enemy units at the battlefield, then moves the friendly unit
• Contested is applied immediately when the enemy unit arrives
• Cleanup occurs: Kai'Sa dies from marked damage
• Control cannot change because the battlefield is contested
• Hidden card remains (not discarded) because the player still controls the battlefield
• Combat is staged
• During the showdown, the player has priority to play the hidden Fae card

Nuances:

• You cannot react with the hidden card during cleanup itself - you must wait until the showdown
• If the moved unit has Assault, it will trigger during the combat because it becomes designated as an attacker when combat is staged
• Contested is applied as a state-based effect when the unit moves, not during cleanup steps
• The hidden card would only be discarded if control was lost, which cannot happen while contested