I have two rules questions:

1. Concussive Blast is turned up as a Boost card. Can I play Backflip to that? If I can, does Backflip cancel only the damage from CB or does it also cancel the damage coming fron the Villain's ATK? In other words, are Boost card effects considered part of an attack (step 3 of an attack in the rules reference)?

2. I set up expert Klaw with Bomb Scare. In step 10 Underground Distribution calls for a minion. Hydra Bomber is put into play. Does its When Revealed ability triggers? Step 10 implies that it does, but elsewhere the rules say that cards PUT into play don't trigger When Revealed abilities. This contradiction makes me suspect that step 10 in the Setup Appendix is poorly written and it is only meant for Schemes and Villains abilities.

The same question could be asked if Weapons Runner is put into play. Granted that Surge is a keyword, but isn't it just an abbreviation for a common When Revealed ability?

1. The damage from Concussive Blast is separate from the attack, so you cannot use Backflip on it.
2. "When revealed" abilities are normally resolved only when cards are revealed (which applies to new villain stages, new main schemes and during step 4 of the villain phase). Step 10 of the setup sequence adds a case where those abilities resolve.
3. Keywords are abbreviations, but not for "when revealed" abilities (they are keyword abilities). Surge would not be resolved from a minions put into play by Underground Distribution.

53 minutes ago, Boofus said:

1. Concussive Blast is turned up as a Boost card. Can I play Backflip to that? If I can, does Backflip cancel only the damage from CB or does it also cancel the damage coming fron the Villain's ATK? In other words, are Boost card effects considered part of an attack (step 3 of an attack in the rules reference)?

Concussive Blast’s boost is not considered part of the villain’s attack, it is a separate effect. Because it is not an attack you cannot use Backflip on it to cancel the 1 damage.

53 minutes ago, Boofus said:

2. I set up expert Klaw with Bomb Scare. In step 10 Underground Distribution calls for a minion. Hydra Bomber is put into play. Does its When Revealed ability triggers? Step 10 implies that it does, but elsewhere the rules say that cards PUT into play don't trigger When Revealed abilities. This contradiction makes me suspect that step 10 in the Setup Appendix is poorly written and it is only meant for Schemes and Villains abilities.

I agree that step 10 implies that it does but I think your reasoning is correct. Cards that are “put into play” are not revealed so their effects do not trigger. Edit: Or maybe not, see the answer above.

53 minutes ago, Boofus said:

The same question could be asked if Weapons Runner is put into play. Granted that Surge is a keyword, but isn't it just an abbreviation for a common When Revealed ability?

Surge is a keyword but not a “when revealed” ability, even though it acts a lot like one. For example, Spiderman’s Enhanced Spider Sense does not prevent the surge effect. Again, surge happens after revealing the card so it does not occur if the card is “put into play” and isn’t a when revealed effect anyway.

I hope that helps! Sorry I don’t have a definitive answer for the second question.

Thanks guys.