When playing Thousand Tailed Watcher, do you have to pay deflect costs, can its effect be counterspelled, or do you need to exhaust a card to use its ability?

Ruling: Thousand Tailed Watcher's ability does not require paying deflect costs because it does not target. It cannot be countered by "counter a spell" effects because it is a unit ability, not a spell card. You do not need to exhaust it when you play it since it is an "on play" ability (unless you haven't paid accelerate or units don't enter ready).

Nuances:

• Counter spell effects only work on spell cards, not unit abilities
• There are currently no cards that can counter unit abilities in general (though a future card was mentioned that counters abilities that target units you control, which still wouldn't affect Thousand Tailed Watcher since it doesn't target)