Jogurt from Shining Force comes close. A hamster with 1 HP, 1 ATK, 1 DEF, and can never gain levels to get any stronger. He at least manages to deal 1 damage when attacking though, so there are worse things out there..just not by much.
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You know what they say: If you can't beat them, join them. If you can't join them, burn their house to the ground!