This morning there's been a Monster Hunter 4 Direct, and they have shown that Nintendo-Capcom collaboration.
Mario & Luigi costumes for the Felynes:
From cvxfreak's Twitter:
You can download the Mario & Luigi Collaboration Quest at Seven Eleven and then via internet afterwards. More details coming later.
Here's a video with both parts. It starts with the Felynes and the Zelda part starts around minute 1:09: http://www.youtube.com/watch?v=oiRJE1Q_gN8
Also Nintendo guild cards:
Iwata twittered additional collaboration-infos: Custom Guildcard-backgrounds and poses: