Am I correct that with this Mags I can have any format-legal Brotherhood of Mutants character on my sideline and so long as it meets the conditions (a BoM character is KO'd of more points than the Sidelined character and Mags is alive to have the effect used) I can generate it on Click 1 and use as normal (unlike an ID card).

Also further assuming I could have multiple options in place that meet the criteria and choose the best-fit for the situation upon triggering the Recruiter Power Action?

Sounds right to me. I haven't been too fond of the recruiter tag for tournament play because your opponent scores them immediately. Otherwise I think you are spot on the money.

100% my concern as well, you'd need to be in a position where the point differentiation is worth it for what you can bring in and the game state it can assist in changing

I was wondering about bringing in pieces from the sideline using the secret identity keyword then using watcher to swap out the new unit for a beefy cousin.

EX: using secret identity Mary Jane to bring in the corresponding Iron Man on its crappy 3 click dial. BUT since that Iron Man is 60 points It can be swapped back to the sideline (using 25pt Watcher's Ponder ability) for a beefy 60 point or less Iron Man on its first click. A bit mechanical but in the end getting 60 points of clix in trade for much less on the team build.

Just haven't found the right trade off yet.

You're correct, and Johnny V brought up why Recruiter is a bad power. The only really good option for so far that's been in Modern was Dr. Strange bringing in Wendigo.

This is... difficult to get to work.

From the Comprehensive Rulebook:

Section 2.6:

From 2.6A

To go with your specific example:

You're going to need a reason to have that non-MJ Iron Man on the Sideline, and the Watcher won't cut it unless you have another Iron Man on your starting force already.

Interesting, I never got that from reading the rulebook. So you're saying sideline characters must have a reason to be there?

Yes, see what I quoted from 2.6 and 2.6A. I think it's one of the dumbest rules in Heroclix; it means that a figure can't be there for, say, both a swap and a recruiter effect.

This is the critical part:

This means you can't chain different replacement effects together. If MJ uses Secret Identity to be replaced with Iron Man, that Iron Man is forever associated with Secret Identity, so it can't later be used by The Watcher's effect, since that would require it to re-enter the Sideline.

In fact, you have to declare that that Iron Man is associated with Secret Identity right from the start, so only Secret Identity will be able to use it.

Hypothetically speaking, if you had two different replacement effects both named "Secret Identity", then they would count as the same effect, and you could use them both on the same figure.
That's why Shifting Focus characters can keep swapping back and forth. It all counts as one effect.

Thank you for the explanation that makes a lot of sense.