Rare have announced
that by playing Crackdown 2, Perfect Dark XBLA will unlock a new character, Agent 4.
Basically, when Perfect Dark detects a Crackdown 2 save game on your Xbox 360 it will make available a new character, Crackdown 2's Agent 4, for multiplayer use.
Crackdown 2 is out in Europe on the 9th July. A demo is now available.