You know, I was playing Perfect Dark the other day, and thought to myself, "Man, you know what this game needs? More Crackdown cameos".
And whaddya know. Here we are. With a Crackdown unlockable now available within Perfect Dark XBLA. Now if only I'd actually thought that, instead of using it to set the scene!
The unlock works like this: if you own Perfect Dark XBLA, and a copy of Crackdown 2, the former is able to detect save games from the latter. If it does so, it makes "Agent 4" available for Perfect Dark multiplayer battles.
That's it! No cars, no rocket launchers, just a guy in a suit. But hey, he's free!