When the Slyren reaches 100 MPH, it starts singing within a few seconds of its transformation. Those who are within its range fall asleep. It can also sing while in protoform, as seen in "Snowdance" that a nest of the Slugs keep the Ice Ogres hibernating. Eli used the one that he caught to put all the Ogres back to sleep. Pronto used Eli's Slyren to save Danna Por from The Gentleman's Geoshard. It is a very powerful slug, as it can break the crystal of a Geoshard and put the Ice Ogres to sleep, and can easily put someone to sleep.
When transformed, the Slyren has the ears of a bat, frog-like arms, and a fishtail. It has a yellow-coloured belly but it's mostly coloured blue. Its tail and mohawk are coloured turquoise.
- Protoform Abilities - Perimeter alarm, can mimic sounds.
- Whistleer - Flies rings around opponent, create a sustained, ear-splitting scream.
- Sleepytime - Strange trilling call puts opponent to sleep.
- Blammerang - High-speed sonic boom blast.
- HyperSonic - Creates a high pitched frequency that causes temporary deafness in an opponent.
Whistleer can stun an opponent with its screams, distracting the opponent and giving the slinger the upper hand if he/she acts fast enough. Sleepytime allows the slinger to make a quick getaway without harming the opponent. This move is also very useful against Ice Ogres, Ghoul Slugs and other large group of animals like a swarm of Bees. Blammerang helps the slinger to attack his/her opponent from afar. HyperSonic is similar to Whistleer but causes more damage. This attack is possibly the one that can shatter Geoshard's crystal.
- Hyperflash - "Narwhaddle" + "Slyren"- TBD. It hasn't officially appeared on the show yet.
- The New Kid Part 2 (First appearance)
- The Gentleman and the Thief
- King of Sling
- Keys to the Kingdom
- The Thrill of the Game
- It Comes by Night
- Dark as Night
- Slugterra: Eastern Caverns
- The Return of the Eastern Champion
- The Slyren is a play on "Siren". The Sirens are female sea monsters that originate from Greek mythology. The Sirens would sing and lure sailors to dangerous waters, which would lead to their deaths. Sirens are also a type of swamp dwelling legless amphibian.
- A Slyren can be seen among Twist's Slugs after revealing his alliance with Blakk.
- Only other Slugs are immune to their singing.
- A Slyren is the only Slug that can break a Geoshard's crystals.
- A Slyren's voice can affect Ghoul Slugs.
- One was seen being ghouled in "Dark as Night". Neither its Ghouled protoform or its velocimorph has been seen in the show, though.
- It is shown that only their singing can return Ice Ogres back to hibernation.
- Trixie used one in the Slugisode "Pack Your Slugs!".