If Vayne attacks with Assault, takes 4 damage from Void Seeker (leaving her at 1 health with Assault's +3 might), then Ride the Wind moves her to an empty battlefield, does she die from losing Assault?

Ruling: Yes, Vayne dies. When moved to an empty battlefield, she loses her attacker status because only one combat can be active at a time, and the second combat remains pending until the first resolves. Without attacker status, she loses Assault and dies from the marked damage.

Sequence:

• Showdown 1 is active with Vayne as attacker (5 might with 4 damage marked)
• Ride the Wind moves Vayne to another battlefield
• A cleanup step occurs after the move is completed
• Vayne loses attacker status because the second combat cannot start while the first is still active
• Vayne loses Assault, dropping to 2 might
• Vayne dies from having lethal damage before the second showdown could begin

Nuances:

• If a unit is moved to base instead of another battlefield, it would no longer be a valid target for effects that require the unit to be at a battlefield
• There can never be more than one combat active simultaneously; additional combats remain pending until the current one completes