Before the beginning of the game’s first turn, the player playing Communication Breakdown chooses one combat value; that combat value cannot be modified during the game. When rolling a six-sided die for Leadership, subtract 1 from the result.

So, if I read that right, you can choose defence and nerf Energy Shield and Combat Reflexes in one shot?

It also negates the hindering terrain bonus!

I would have hoped they had worded it so it meant non-powers (i.e. team abilities and feats) and that it disallowed subsituted values

Frankly, the way it is worded makes no sense (oh no, my energy shield won't come up because my radio doesn't work but the Fantastic Four is still their usual perfectly coordinated machine!)

That's a good point. It seems like the spirit might have been to somewhat nerf Perplex, but the wording certainly leaves open many possibilities.
And along the same lines as your example, if I choose Damage, there goes your RCE or CCE which seems kind of silly for something titled Communication Breakdown. "I've lost communication and now have forgotten how to fight with my usual expertise."

I think they left replacement values alone since that would have opened up a can of worms playwise - whenever a velue is halved, that is a replacement.
So if CB had affected replacement values, that would mean that you could choose movement and be able to do full move Charges and Running Shots, and to move out of hindering at full speed. Or, you could choose range and not have to halve it when doing a HSS attack or a Pulse Wave.
Frankly, I'm glad they let replacement values out of the mix. If you want to screw over replacement values, use Isolation.

Good points, Quebbster. I hadn't looked at those options regarding replacement values. Of course, I never find the useful loopholes anyway so I guess that's not too surprising.

Well, I've had to shoot down a few hopefuls who thought the card worked that way already...

The card can also hose a Hydra/Police team and effectively say "No, 2000AD/Alpha Flight/Ultimate X-Men, you -don't- get that +1 to attack."

Unless you build a team with no modification powers or TAs, you're going to get hosed by it somehow. Your best bet is to include a variety of modifiers and just somewhat hampered rather than stick everyone with defense modifiers and get blown out of the sky.