If I move a unit to a battlefield and the enemy plays Ride the Wind on an Irelia Fervent into that battlefield, can I then play Arcane Shift to damage Irelia for 3, banish a unit, and play Vex to the same battlefield?

Ruling: You cannot use Arcane Shift to banish one unit and play a different unit like Vex. Arcane Shift requires you to banish a friendly unit and then play that same unit back. Additionally, because Irelia has [Deflect], you must pay an additional [A] (any domain rune) to target her with Arcane Shift's damage.

Sequence:

• Ride the Wind resolves (moving Irelia to your battlefield)
• Chain resolves and state returns to OPEN
• You regain Focus and Priority
• You can now play Arcane Shift (starting a new chain), paying the additional [A] cost to target Irelia
• Arcane Shift banishes your chosen friendly unit and plays that same unit back
• The banished unit can be played back to the contested battlefield since you are now in combat there

Nuances:

• Arcane Shift is [ACTION] speed, so it cannot be played in response to Ride the Wind (which is [REACTION] speed). It can only be played after Ride the Wind fully resolves when the state returns to OPEN.
• You need both Focus and Priority to play Arcane Shift after Ride the Wind resolves.
• If you want to play Vex, that would be a separate action entirely, subject to standard playing rules.