How does countdown work when attacked by a tractor beam? Does he cancel everything as long as he takes a stress?

He can.

"When defending, if you are not stressed during the "Compare Results" step, you may suffer 1 damage to cancel all dice results. if you do, receive 1 stress token."

So when Countdown is shot at, he may choose to take a damage and a stress and then the Tractor won't hit.

He can, but he'll still suffer take the damage and still get the stress.

Indeed. Equally, when he (would be) hit with an ion cannon or ion pulse missile, he can effectively change the ion token(s) to a stress token if the latter is more palatable to deal with.

Essentially, because Countdown's ability 'interrupts' the attack at the 'work out whether you hit' stage, so there are no uncancelled hits left when you figure out if the attack hit, the attack is considered to have missed , but Countdown takes a point of damage and a stress token instead.

This means:

• If you trigger countdown, you will never suffer "if this attack hits" effects, except against Lieutenant Blount (who still hits even if you have no uncancelled hits) - theoretically you can use countdown's ability against an ion pulse missile fired by blount....but all that achieves is to make you take 2 damage and 2 ion tokens and a stress token!
• If you trigger countdown, the attack misses, so 'after an attack that missed' effects, like gunner, IG-88B and Bossk do come into play.
• Since you cancelled the results (albeit not with defence dice), results which trigger off you cancelling red dice (like the Imperial version of Kath Scarlet) would apply.

Also keep in mind it backfires if used vs an advanced homing missile as well.

Because it's a "if this attack hits deal a faceup damage card" and not a true critical hit,using countdown would result in a 1 damage, a faceup damage and a stress.

1 hour ago, Ralgon said:

Also keep in mind it backfires if used vs an advanced homing missile as well.

Because it's a "if this attack hits deal a faceup damage card" and not a true critical hit,using countdown would result in a 1 damage, a faceup damage and a stress.

No if countdown triggers his ability the missile will miss.

7 hours ago, Ralgon said:

Also keep in mind it backfires if used vs an advanced homing missile as well.

Because it's a "if this attack hits deal a faceup damage card" and not a true critical hit,using countdown would result in a 1 damage, a faceup damage and a stress.

Only if Blount is firing the missile...and one would hope that whomever is playing Countdown is intelligent enough to know when, and when not, to use his ability.

Frankly I'd take the tractor beam hit this thread started off with, even if you get boosted into R1 of a TIE/D with full modifiers (say Vessery?) you can always just use your ability on that primary weapon attack rather than take a damage from a weapon that isn't going to hurt you otherwise...

2 hours ago, ZealuxMyr said:

Frankly I'd take the tractor beam hit this thread started off with, even if you get boosted into R1 of a TIE/D with full modifiers (say Vessery?) you can always just use your ability on that primary weapon attack rather than take a damage from a weapon that isn't going to hurt you otherwise...

However, if the tractor beam would drop Countdown on an asteroid, thereby preventing return fire, it might be wise to use the ability.

1 hour ago, HungryFFG said:

However, if the tractor beam would drop Countdown on an asteroid, thereby preventing return fire, it might be wise to use the ability.

True, I suppose sometimes it is unavoidable - typically like to stay away from obstructions when tractor beams are on the table but, alas, sometimes it will be unavoidable.