Does Arcane Shift require a valid enemy unit target to deal 3 damage to in order to be played, or can it be played just to blink a friendly unit when no enemy units are at a battlefield?

Question

Accepted Answer

You must have a legal enemy unit at a battlefield to choose as the target for Arcane Shift when you place it on the chain. If no such enemy unit exists at the time you finalize the spell, you cannot play Arcane Shift (because you cannot make the required target choice). If you do choose a legal enemy unit when playing it and that target becomes illegal before resolution, the Deal 3 instruction will simply do nothing while the rest of the spell still resolves as able.

You cannot play Arcane Shift solely to blink a friendly unit if there are no enemy units at a battlefield to be chosen as the target for the "Deal 3 to an enemy unit at a battlefield" instruction. You must be able to choose a legal enemy unit at a battlefield when the spell is finalized. If you do choose a legal enemy unit and it becomes illegal before resolution, the damage instruction will be ignored while the banish/play instruction still resolves as able.

When you attempt to play Arcane Shift, you must finalize the spell by making any choices it requires; that includes choosing which friendly unit to banish and choosing an enemy unit at a battlefield to be dealt 3 damage if such a target is required by the spell text [355.10.d.2]. If there is at least one legal enemy unit at a battlefield, you may choose one as the target and finalize Arcane Shift. If that chosen enemy unit becomes illegal before resolution (for example moved to base), the damage instruction will do nothing but the rest of the spell still resolves as possible [359.3.e.5] [359.3.e.7]. If there are no enemy units at a battlefield at the time you would need to choose the target, there is no legal choice to make for that instruction and you cannot complete the required choice to finalize the play of Arcane Shift (under the standard targeting/choice process implied by the rules) — therefore you may not play it purely to blink a friendly unit in that situation (see assumptions). If you successfully play Arcane Shift and the banish/play instruction resolves, the banished friendly unit will be played ignoring its cost and legal placement choices for that play will follow the usual rules and examples (see [FAQ:unleashed#16] for an Arcane Shift example).

If you can make a legal choice for the enemy target when finalizing Arcane Shift but the chosen enemy unit changes zones to a non-board zone before resolution, it severs the targeting relationship and will not be affected by the Deal 3 instruction (see rules on targets changing to or from non-board zones) [359.3.e.5]. If the chosen enemy unit is moved to base (a board zone) before resolution, the target relationship remains but the instruction’s targeting restrictions may make it illegal to affect that object at resolution and the damage will be ignored [FAQ:unleashed#22] [359.3.e.7].

The text of Arcane Shift contains two sequential instructions: banish a friendly unit and then its owner plays it ignoring cost; and Deal 3 to an enemy unit at a battlefield. The Deal 3 instruction is a targeted instruction that requires choosing an enemy unit at a battlefield when the spell is finalized. Under the targeting/choice principles in the Core Rules, a spell that includes a target-like instruction must have that choice made when it is placed on the chain (see the general treatment of targeted instructions and examples such as "Kill a unit at a battlefield" that always target a unit) [355.10.d.2]. Because you must make the required choices during finalization, you need a legal enemy unit at a battlefield to select as the target for the Deal 3 instruction in order to finalize playing Arcane Shift. If no such enemy unit exists, there is no legal target to choose and, given the lack of any provided exception in the supplied rules, you cannot complete the required choice and therefore cannot play the spell (see assumptions). If you do choose a legal enemy unit when you play Arcane Shift and that chosen unit later becomes illegal before resolution (for example it is moved to base or somehow stops meeting the targeting restriction), the Deal 3 instruction will simply have no effect on that target as the spell resolves, while the rest of Arcane Shift resolves as it can [359.3.e.5] [359.3.e.7]. The official example for Arcane Shift in the FAQ confirms that the banish/play part can put the unit pending on the chain and that finalization choices for playing the banished unit follow normal rules [FAQ:unleashed#16].