Siren (also known as the performer Syren) is a beautiful ghost with a magic singing voice and is the antithesis of her sister Banshee. She keeps her sister young by draining the youth of her listeners and feeding it to her.
According to Irish folklore, the Glostic Sisters were a pair of wandering spirits. One was a Banshee, the other a Siren. Banshee requires the youth of mortals to sustain her strength. Siren is the only one who can provide it.  Together they eluded detection throughout the centuries until the 20th century.   In Central Park, Siren found Banshee near a pond and partially rejuvenated her. Hungry for more, Banshee forced Siren to seek out a larger source of youth to take from.
Meanwhile, at the Firehouse, a Subharmonic Acoustic Scanner was rigged to trace Banshee's isolated vocal frequency. The Ghostbusters traced Banshee to a Syren concert, not realizing the connection yet. Due to a limit in funds, only Roland Jackson entered the concert. Siren placed her hypnotic hold on everyone in the audience, including Roland. Luckily, Roland left the concert to help the Ghostbusters trap Banshee. When she was finished stealing the youth of her fans, Siren realized she was too late.
Roland became obsessed with Siren's ecto-acoustics as it directly affects the human brain's pleasure centers and puts them in an enthralled state.  Egon Spengler modified special earmuffs that inversely emulate Siren's vocal patterns, thus nullifying the hypnotic effect.  However, Roland freed the Donkey ghost, Gas ghost, and the Banshee. He was still under Siren's hypnosis and believed she and Banshee belonged together. After Banshee was rejuvenated again, she demanded more youth and took Siren to the Harvey Finkel High School, where a basketball game between the Rams and Trojans were taking place. Invigorated by the youth, Banshee overpowered the Ghostbusters but Kylie Griffin was able to reason with Siren. Siren took back the youth and rapidly aged Banshee into a hag. She then willingly went into a Trap and released her hold on all victims. Banshee then tried to attack Roland but the other Ghostbusters re-trapped her. Siren and Banshee were put into the Containment Unit where it appears they submitted to the authority of Surt. Siren hesitated at first but followed Surt's will and placed a spell on Slimer. At the proper time, Slimer would betray Eduardo Rivera and Surt would make his escape. The plan failed but Surt still had Slimer compromise Eduardo. Siren then released Slimer from the spell.
Unlike her sister, Siren is kind and selfless. She feels no end of sadness from being forced to hurt humans by her cruel sister or the tyrannical Surt.
Egon states a Banshee is an Audio-Sonic Non-Vaporous Free Floating Apparition.  Based on relation and similarity in powers, it is likely Siren has the same classification.
- ↑ Egon Spengler (1997). Extreme Ghostbusters- Sonic Youth (1997) (DVD ts. 09:35-09:44, 10:07-10:13). Sony Pictures Home Entertainment. Egon says: "I'm guessing you didn't make it to my chapter on the Glostic Sisters. According to Irish folklore, they were a pair of wondering spirits. One was a Banshee. The other, a Siren...Banshee requires the youth of mortals to sustain her strength. Her sister is the only one who can provide it."
- ↑ Syren (1997). Extreme Ghostbusters- Sonic Youth (1997) (DVD ts. 02:54-02:57). Sony Pictures Home Entertainment. Syren says: "We've eluded detection all these years."
- ↑ Banshee (1997). Extreme Ghostbusters- Sonic Youth (1997) (DVD ts. 03:33-03:36). Sony Pictures Home Entertainment. Banshee says: "I've taken us this far through the centuries."
- ↑ Egon Spengler (1997). Extreme Ghostbusters- Sonic Youth (1997) (DVD ts. 09:52-10:01). Sony Pictures Home Entertainment. Egon says: "Kylie's right. A Siren's vocal frequency can directly affect the brain's pleasure centers. Within seconds of hearing her sing, you'd be completely enthralled."
- ↑ Egon Spengler (1997). Extreme Ghostbusters- Sonic Youth (1997) (DVD ts. 11:17-11:23). Sony Pictures Home Entertainment. Egon says: "I've reconfigured these to inversely emulate Siren's vocal patterns. That should protect you from the hypnotic effects."
- ↑ Egon Spengler (1997). Extreme Ghostbusters- Sonic Youth (1997) (DVD ts. 04:00-04:04). Sony Pictures Home Entertainment. Egon says: "An Audio-Sonic Non-Vaporous Free Floating Apparition to be precise."