Do I have to declare Tricksy Tentacle targets initially or only on resolution?

To determine when you must declare targets for Tricksy Tentacles, you must declare the targets (the enemy units you intend to move) and the destination location when you finalize the spell onto the chain, not upon resolution.

Ruling

You must declare the targets and the destination location when you finalize the spell onto the chain.

Reasoning

1. Targeting Requirement: According to Rule 355.7, when a card chooses specific game objects to affect, it is considered to be targeting those objects. Because Tricksy Tentacles requires you to choose specific enemy units to move, those units are targets.
2. Move Destinations: Per the Patch Notes (2025-10-24), move destinations are a required choice that must be made at the time of putting a spell or ability on the chain.
3. Timing of Choices: Rule 355.8 states that in order to put a spell on the chain, valid choices must be made for all targets. Therefore, you must select the specific units and the destination location before the spell is finalized and before any player has the opportunity to play reactions.

Summary of Sequence

1. Initialization: You announce you are playing Tricksy Tentacles.
2. Finalization (Targeting): You declare which enemy units are being targeted and choose the destination location. You must ensure the chosen units share a controller and have a total Might of 8 or less at this moment.
3. Chain: The spell is placed on the chain as a pending item.
4. Priority: Priority passes, allowing players to play reactions (e.g., moving a unit out of the battlefield or changing its Might).
5. Resolution: The spell resolves. If the targets are still legal (Rule 359.3.e), the move occurs. If the targets no longer meet the criteria (e.g., their total Might is now greater than 8 due to a reaction), the spell will resolve, but you may need to choose a subset of the original targets that still fulfills the requirements (Rule 355.11.b).

Note: I could not fully verify this ruling against the retrieved rules.