Baldur's Gate : The Sword Coast Chronicles : NWN2 Persistent World

The trollbane flail from the blushing mermaid shop appears to be vanilla. It has the x2 crit multiplier.

Trollbane is a light (offhand) flail. It's stats are correct for its type. Note that these weapons cannot be used in conjunction with Weapon Finesse; they are otherwise identical to shortswords.

i spent a month saving up for it and i didnt notice until my first crit.

I didn't even know they couldn't be used with weapon finesse. Glad I never bought any of those.

RagingPeace - you can try to ask a DM for a refund as this seems to be something that's very easily confused, with there being two different types of flails available.