Uh...that 'mommy' thing is a bit much if you ask me...Not only cliche (which I'm not usually opposed to necessarilly), but also nearly right out of the first five minutes of Chrono Cross...
This boar aint gonna be no average piggy, guys...I'm thinkin' around 3 or 4 feet high, razor sharp tusks...Also, if you really want it powered up, that wouldn't be a problem...The way I was going to handle Hunter & Amy's transformation is going to involve crustational (?) growths (that grow) and something similar could be used on the boar...
Also, like I said, they wouldn't kill it off immediately, it could be injured and then reflexively retreat to the FF, where it could then be defeated...
Perhaps even, Backer could already be somewhat in where the FF is beforehand and instead of them teaming up to defeat it, the boar goes to the safety of the FF's shine and instead meets (runs into, whatever...) Backer and even before Hunter & Amy make it back, Backer has already finished it off...This sounds nice to me...A better introduction than "I'll help you fight that thing you're having trouble with", which, now that I think about it, is going to be used in the Jailbreak when Sigil is helped out against some nasty guards...I don't want us re-using ideas if we can help it...