Chip, the Rat
Chip is an unusually intelligent rat who, upon purchase, will love you unconditionally. Will chitter in your ear and perform a dance on its hind legs to lift your spirits.
Stat block: HP 4, Morale — (loves you too much to leave), No armor, Bite d2 but always causes infection. Very Small, DR16 to hit.
Chip understands you and will follow basic commands. Will also dance for your amusement: roll an additional d4 HP when resting.
Sold by Mikhael the Merchant in Grift for a portion of the buyer's soul. The infection in his bite is the only price he charges; otherwise he is, briefly, the only thing in the world that loves you.
Whether Chip's love survives the death of his owner — and whether the next person down the road inherits a heartbroken rat — is the open campaign-thread.