Consider Farlander against a list that specializes in giving you more than one stress token, perhaps even 5 or 6 in a turn with all the abilities coming into play. Now it's Farlander's turn and he uses his ability to spend a stress to modify his roll. His card explicitly doesn't say "once per turn" as many cards do. We have also already figured out that he doesn't even need focus results to spend the stress token. But how many times can he do this? Say he has through insane means acquired a dozen stress tokens. Can he just spam his ability and remove them all? My confusion stems from two points.

A: the fact that the card doesn't limit how many times he may do this a turn

B: the fact that the card doesn't require him to actually have a die result to modify to spend the token.

Thoughts? Is this a solid counter to panic lists?

The "Once per opportunity rule" covers this. You can only use his ability once each time it can be used, ie. once per attack. So unless you've got a way to generate multiple attacks, you can only ever burn one stress with his ability per turn.

You may use abilities once per opportunity. Keyan is able to spend single a stress token each time he attacks.

Excellent, thank you!

Like spending stress to modify no eyeballs... this is also covered in the same place in the FAQ... in the very next paragraph.