Well, first, I didn't find the 'elven cat' (or anything that was just a 'cat') in The Complete Book of Elves, just to help (or, in this case, I suppose hinder

) that comment (sorry).
Second, I am lead to recall my bard from a game I am still playing in (though as a different character, now) who wanted a riding dog to carry all her stuff for her (since she only had a Strength of 11 and had a LOT more to carry than she could manage on her own). She looked for an intelligent animal, something not as stupid (pardon the opinion) as your common dog. She found it, but it was whole-heartedly apathetic (the DM doing a wonderful job of RPing it). Hence, it was dubed Eor. Every time Eor was accompanying the party in combat, he would give a sigh and give his power-word: a very uncaring "woof". And, interestingly (yes, it was coincidence (though I'm not saying the DM would be out to kill us)), we would always win the battle following this (so developing the 'power-word' idea, that was more just poking fun at it than anything else).
Anyhow, to get to the point, we eventually came to a tough situation that we really couldn't handle. The DM, not wanting us to die horrible deaths (and maybe being a little plot-driven at this point in the game...), had Eor turn out to be a polymorphed (14th level, I think it was) sorcerer, that was willing to help us for finally releasing him from his imprisoned state.
It wasn't a mere 'pull the party out of a tough situation' (though, yes, that was part of it), but also kind of giving a bit of a reason why we got away with so much when Eor would just apathetically say, "woof."
And, it was not at all a 'planned thing from the start.' It just kind of developed (if it seemed otherwise).
I'm thinking I need to add my babbling comment to my sig... Sorry, all. v.v