A vicious animal attacks you on a moonlit night. Friends drive the beast off, but you discover that you've been cursed with lycanthropy, to become a similar beast under the full moon. (work with your DM to determine details)
A strange woman gives you an ornate box sealed with wax and hoarsely whispers "It's up to you now, keep it safe, keep it from ... them." It is not until the woman drops dead at the character's feet that the dagger in her back becomes obvious.
After a mighty storm has passed, You discover a old waterlogged chest, sealed with chains and weighted with stones. You find drowned form of a young animal. Suddenly, the creature's eyes open you have acquired an unusual pet.