Can an illegal target that will become a legal target before the spell resolves be targeted?

Question

The interaction I'm wondering about is between Bounding Krasis, Harbinger of the Tides, and Collected Company.

As a part of Collected Company's resolution, two creatures may enter the battlefield at the same time. If both these creatures have ETB triggers, the controller gets to choose what order they go on the stack.

Harbinger of the Tides has an ETB trigger that reads:

When Harbinger of the Tides enters the battlefield, you may return target tapped creature an opponent controls to its owner's hand.

Bounding Krasis has an ETB trigger that reads:

When Bounding Krasis enters the battlefield, you may tap or untap target creature.

If a Bounding Krasis and a Harbinger of the Tides entered the battlefield at the same time due to a spell such as Collected Company, would the controller be able to target an untapped creature with Harbinger's trigger and then tap it with the Krasis trigger on top of it on the stack?

Answer 1

You can't choose to target an illegal target. Period. When the Harbinger of Tides enters the battlefield, it can only target creatures that are tapped at that time.

---

To be specific, the following rules are relevant:

• 603.3. Once an ability has triggered, its controller puts it on the stack as an object that’s not a card the next time a player would receive priority. [...]

[...]

• 603.3d The remainder of the process for putting a triggered ability on the stack is identical to the process for casting a spell listed in rules 601.2c–d. If a choice is required when the triggered ability goes on the stack but no legal choices can be made for it, or if a rule or a continuous effect otherwise makes the ability illegal, the ability is simply removed from the stack.

• 601.2c The player announces his or her choice of an appropriate player, object, or zone for each target the spell requires. [...]