Nippon Ichi is staging some collaborations for PSP's Classic Dungeon X2, which sees release on 3/24.
Dengeki reveals that the game will have collaborations with Falcom properties Ys, Zero no Kiseki, Sora no Kiseki and fellow Nippon-Ichi property Phantom Breaker.
I'm not sure what the collaborations are just yet.
It also looks like the the game may have a collaboration with Mr. PS3. I don't know who Mr. PS3 is.