If I use Arcane Shift to blink my only unit at a battlefield I control, can I play it back to that same battlefield?

Ruling: You cannot play the unit back to the same battlefield unless you are in combat at that battlefield. When you blink your only unit, you lose control of the battlefield during the cleanup step that occurs between Arcane Shift resolving and the unit being finalized to the chain.

Sequence:

• Arcane Shift resolves and instructs you to play the unit (adding it as pending to the chain)
• A cleanup step occurs
• During cleanup, since you have no units at the battlefield and are not in combat there, you lose control of it
• The unit finalizes to the chain, but you no longer control the battlefield so cannot play it there

Nuances:

• If you are in combat at the battlefield (it is contested), you maintain control throughout the showdown and can play the unit back
• Arcane Shift requires targeting both a friendly unit AND an enemy unit at a battlefield - you cannot play it without valid targets for both
• "Do as much as you can" only applies during resolution, not when initially targeting the spell
• You can Arcane Shift a unit from one battlefield and play it to a different battlefield you control