Sirine (Shadows of Amn)

The Sirines in Shadows of Amn are subjects of the fairy queen Vaelasa, whose realm is located in the Windspear Hills.

Only putting the party at odds with Vaelasa will let two of them appear at all.

Involvement
Two sirines will back Vaelasa in the southeastern Windspear Hills if Gorion's Ward attacks the fairy queen.

Helping Irenicus's captive dryads
Other than by attacking her, the fairy queen will also turn against the party if her fellow dryads were killed in Irenicus' Dungeon.

Combat

 * See: Sirine

The only notable difference between the two Shadows of Amn sirines and the more common variant, as found in the first games of the series, is their race: because they are technically basilisks rather than fairies, certain items or spells with specific abilities related to these races will not behave the same as in other fights against sirines.

Bugs

 * Instead of being a fairy, the Baldur's Gate II sirine is of the race basilisk.