Sometimes I look up certain pets and it'll say "Legacy" in parenthesis under the adoption date. Also, there's a section in the Achievements list called "Legacy" and it's unclear what these are for. Would someone mind letting me know what all that is about, please?

Legacy pets were created before October-November 2009.

Legacy achievements are from the first achievement system and are no longer attainable.

Ah, I see. Still, sad that we can't do some of the achievements though.