Amphibious. The sirene can breathe air and water.
Magic Resistance. The sirene has advantage on saving throws against spells and other magical effects.
Spellcasting. The sirene casts one of the following spells, requiring no material components and using Charisma as the spellcasting ability (spell save DC 13):
1/day each: crown of madness, fog cloud, invisibility
Multiattack. The sirene makes two Dagger attacks or two Shortbow attacks.
Dagger. Melee Weapon Attack: +6 to hit, range 5 ft., one target. Hit:6 (1d4 + 4) piercing damage plus 3 (1d6) cold damage.
Shortbow. Ranged Weapon Attack: +6 to hit, range 80/320 ft., one target. Hit:7 (1d6 + 4) piercing damage.
Sirene's Song (2/Day). The sirene casts suggestion with a range of 1 mile that affects all creatures of the sirene's choosing in range. Each target has disadvantage on the saving throw.
Sirenes are seen in only a few places in Faerûn. Obviously, the Sword Coast region is one such place. Sirenes have also been sighted in the Sea of Fallen Stars and the Moonsea lake. There are rumors that sirenes can be found at the courts of storm giant lords.