Can Beast Below's "when you play" trigger be put on the chain if you control no other friendly unit to target?

Question

Accepted Answer

No. The triggered ability of Beast Below ("When you play me, return another friendly unit and an enemy unit to their owners' hands.") cannot be placed on the chain if you cannot choose a valid "another friendly unit" (or cannot choose a valid enemy unit). Target choices for the trigger must be made when the triggered ability is placed on the chain, and you must have valid targets to do so [355.5.b] [355.8] [355.9].

You may not put Beast Below’s "When you play me, return another friendly unit and an enemy unit to their owners' hands." trigger on the chain if there is no valid "another friendly unit" to choose (or no valid enemy unit). The trigger can only be placed on the chain when you can make the required target choices [355.5.b] [355.8] [355.9].

You play Beast Below. Its triggered ability "When you play me, return another friendly unit and an enemy unit to their owners' hands." triggers and is put into the pool of triggers. When that trigger is being finalized to be placed on the chain, you must make target choices for its instructions (targets are chosen when the triggered ability is placed on the chain) [355.5.b] [355.8]. To finalize the trigger you must choose a valid "another friendly unit" and a valid "enemy unit". A valid target must meet the targeting criteria and be an appropriate object on the board [355.9]. If no valid "another friendly unit" exists (for example, you control no other units), you cannot make the required choices and therefore you cannot place the trigger on the chain [355.8] [355.9].

If a valid target appears after the trigger generated but before you finalize triggers (e.g., an opponent or you play or move a unit into a valid state), you can choose it when finalizing and thus place the trigger on the chain [355.5.b] [355.8]. If you successfully choose valid targets when finalizing the trigger but one or both targets become illegal by the time the trigger resolves, the resolution will ignore the illegible instruction(s) as appropriate (instructions that can't be followed are ignored) [359.3.e.6] [359.3.e.11]. If a chosen unit moves to a non-board zone (e.g., is banished or returned to hand) before resolution, it ceases to be the same object and the targeting relationship is severed; that target will be treated as invalid at resolution [359.3.e.4] [FAQ:unleashed#22]. If Beast Below were played from Hidden, Hidden-specific rules may restrict which targets can be chosen for play effects/abilities that choose targets from the battlefield where it was played; the provided Hidden rulings are limited, so this ruling assumes a normal (non-Hidden) play [811.1.d.2] [811.2].

When you play Beast Below, its text "When you play me, return another friendly unit and an enemy unit to their owners' hands." is a triggered ability that triggers when the unit is played. Target choices for triggered abilities are not made at the moment you play the unit; they are made when the triggered ability is being placed on the chain [355.5.b]. The rules require that in order to put any spell or ability on the chain you must make valid choices for all targets at that time [355.8]. A valid target must be an appropriate game object on the board that meets the targeting restrictions (for example, "another friendly unit" must be a different friendly unit on the board) [355.9]. Therefore, if you control no other friendly unit (so there is no valid "another friendly unit" to choose), you cannot make the required target choice and cannot place the trigger on the chain [355.8] [355.9] [355.5.b].

If a valid target appears before you finalize triggers, you may then choose it when finalizing and place the trigger on the chain [355.5.b] [355.8]. If you do choose targets and later, before resolution, a chosen target becomes illegal or moves to a non-board zone, the resolution will treat that instruction accordingly (instructions that can't be followed are ignored) and moving to a non-board zone severs the original targeting relationship [359.3.e.6] [359.3.e.4] [FAQ:unleashed#22].

Because Beast Below's instruction requires two specific targets ("another friendly unit" and "an enemy unit"), both must be selectable when the trigger is being finalized. If either is missing at that moment, the trigger can't be put on the chain.