Questions, If I were to use Force blast with Cosmic spider-man:

ENIGMA FORCE BLAST: Cosmic Spider-Man can use Force Blast. If he does so, he can then use Ranged Combat Expert as a free action targeting the same character.)

While using the Whirlwind feat:

Prerequisite: Force Blast
Choose a character.
When the character uses Force Blast, the result of
the six-sided die roll can be split among multiple
target adjacent opposing characters. The targets are
otherwise affected normally by Force Blast.

Would I be able to use Ranged Combat Expert on all the targets I hit with force blast?

Thanks in advance!

Yes. You can use RCE against all the characters you FB'd assuming they all got knocked away and CSM wasn't in base contact anymore.

Would you make one attack roll or one per character you knocked back?

Ranged combat expert only ever targets/attacks a single character. You'd have to attack each one separately.

You say "have to," as if dealing 5-7 damage each to multiple consecutive opponents was a bad thing.

It is if you roll some critical misses

While this is out there, if Cosmic Spider-Man is adjacent to multiple opposing characters and has Whirlwind and Elite Sniper attached, can he designate 0 knockback to a character so that he can attack it with RCE?

If he has a character adjacent to himself he can't make ranged combat attacks and thus can't use the RCE.

That's what the Elite Sniper (Sharpshooter ability) is for.

But with Elite Sniper, he gets the Sharpshooter ability and CAN make ranged combat attacks against adjacent characters.

This came up in a previous discussion, so I'll just quote normalview's answer from that thread:

I guess I was asking more...do we need a Final Word on this? (normalview's answer seems to be more how he would rule it if the issue came up and not a definitive answer. Or is that the Final Word answer?)

Bah, I somehow totally skipped over that Elite Sniper part. Heck, I was thinking of adding "But he could if he had Elite Sniper on him".

Must wake up throughly before browsing the Realms it seems.

I thought in order for a character to use a feat he needed the actual ability not a white power that let's him use said power.

To use a feat you need to be able to use the prerequisite. Possessed on the dial, used through a trait or SP or from a relic or resource: all good.

Or are hitting multiple Mystics figures.