I believe I mentioned something earlier in the thread, but here's something a bit more detailed...The story starts with Bloo obsessing about zombies wanting to eat everyone's brains and take over the world. Right about then a kid Mac's age arrives wanting to adopt an IF - Bloo insists that he's a zombie there to eat everyone's brains. Ignoring Bloo (who tags along), Mac starts showing the kid around. They encounter Wilt, Coco, and Ed seperately while on the tour and the kid expresses interest in adopting each of them, to which Bloo reacts by telling him what lousy brains they have, trying to dissuade him from adopting them. At the end:
Spoiler Below the kid imagines up his own combination of Wilt, Ed, and Coco and goes his merry way, and the others accuse Bloo of trying to deter the kid from adopting them not because of zombies but because he loves them and doesn't want them to leave.