The Moon Rings store moonlight and only works in a place that can receive full moonlight, such Lyla used it to open the Trident Cave, but it did not work inside. When the mermaid graduates in the Mermaid School, she is given a Moon Ring and is initiated in their respective pod. If a mermaid loses her Moon Ring, it will be near impossible to receive a new one unless they can prove to their respective mermaid council their worth.
The mermaid trio's use of magic in close proximity to the ring caused its stone to glow and release a beam which stunned Rita. However, the properties of a moon stone can be altered, like the trident's which was altered to absorb a mermaid's energy rather than react to it.
It was Aquata's Moon Ring that allowed Nixie, Sirena, and Lyla to get legs. Rita later teaches the girls to use the Moon Ring's power when she agrees to help them.
It is implied that the Moon Rings need to be placed in shells to function. Improper use of powers or less powers than required is also implied to cause problems, as seen when Lyla and Sirena attempted to stop a rainstorm using the Moon Ring without Nixie, causing snowfall indoors. The rings' source of power is placed within the moonstones. Moon Rings also depletes over time, and to load them, they have to be exposed to the light of the Full Moon, or another object that stores full moonlight, such as the Trident.
- Rita Santos (formerly)
- Aquata (got a second one)
- Mermaid Pod members (majority)
- Unnamed Mermaid (formerly)
- Evie McLaren (formerly)
- Healing- The rings have the power to heal as shown when the girls (Sirena & Nixie) and Rita were able to heal Lyla when she was accidentally zapped by the Trident.
- Chlorokinesis (Plant Manipulation)- It can also be used to grow/manipulate plants as Rita made the seaweed grow and this could be used to provide camouflage, and the same thing could also be used on a kelp forest as stated by Rita.
- Force Field- It could be used to provide a magic shield/force field, like in "Decision Time", the girls used their Moon Rings at the same time to prevent Cam from being turned into a merman and taking over Mako.
- Coma- They also seem to have the ability to put people into a type of coma as seen in "Moon Ring 2" when the girls were trying to get the moon ring from Zac, they accidentally used their powers on the moon ring and the blast hit Rita, knocking her unconscious.
- Legs Spell- Mermaids can perform a spell to grow legs, but that spell is only possible on a Full Moon. As the Moon Rings store moonlight, it is possible to a mermaid to perform this spell without it. It's not known if this spell is reversible, but most likely is.
- Enlargement Spell- Merpeople can perform a spell to enlarge an object like when Mimmi used the Moon Ring to make the crayfish bigger.
- Shrinking- Merpeople can shrink objects. Mimmi shrunk the crayfish after making it too big and Evie accidentally shrunk herself when trying to remove the ring from her finger.
- Duplication Spell- Merpeople can perform a spell to duplicate matter in number. Mimmi and Ondina performed the spell successfully.
- Sleep Spell- Merpeople can perform a spell to make someone fall asleep. Ondina performed the spell on David after he was enchanted by Sirena's song.
- Containment Spell- Merpeople can perform a spell to contain things. Weilan has a puzzle box in her apartment to contain dangerous spells. Mimmi used it on a puzzle box along with a shrinking and adapting spell.
- Adapting Spell- Merpeople can perform a spell of adaptation. Mimmi performed the spell along with a shrinking spell on a Chinese puzzle box.
- Incineration- Merpeople can perform a spell to incinerate objects. Mimmi and Ondina performed the spell successfully to destroy a Chinese puzzle box enchanted with shrinking and adapting spells.
- Object Manipulation- Merpeople can perform a spell to manipulate objects. Ondina performed this spell to demonstrate the moon ring's power to Evie, who then enchanted a mop to clean the floor. When the mop got stuck in the bucket, she boosted it with extra power, making it spin out of control.
- Levitation- Merpeople can perform a spell to make objects float in midair. Ondina demonstrated it to Evie, who then did the same thing, but found herself unable to undo it.
- Storm Spell- Merpeople can perform a spell to summon a powerful and strong storm full of thunder and lightning.
- The Trident and the Moon Ring shares the same stone, but the only one in the Trident is much bigger, thus the power of the Trident is more powerful than the Moon Ring.
- A mermaid only gets her Moon Ring when their training is complete in Mermaid School and they are initiated into the Pod.
- It is not known what happens if a land person is wearing the ring on a Full Moon, but it probably would be dangerous, as stated by the girls.
- While very similar in look and function, the Moon Ring stone is different than the Crystal Necklaces stone.