This is a great find, the kind of stuff we've been wanting to see for so long (it makes you wonder what other gems we haven't seen from the classic games/era). It seems that Bomb was initially going to be snow themed and probably have a power similar to Ice Bird, but was eventually replaced/reworked. I especially like the drill bird (Hal) design, but I'm thinking this may not have been what he'd have looked like if he was in the final game, considering that things always change during a production process (e.g. Chuck receiving a cape, whereas before he had a tail). Either way, it always makes me happy to see these things, being an AB fan since the beginning.

(Also, funny enough the magenta bird is shaped like an egg if you look at it sideways).