This pet will produce a Colorful Star Jelly Potion, and energy potion that produces Colorful Star Jellies when taken. However, this comes at cost of 180 coins per Potion production. If there are not enough Coins, the pet will not produce Potions.
One of the extra advantage of owning the pet is her Power+ effect, Serenade of Love. It will create five small health potions worth 10 Energy and heart-shaped rings of Bear Jellies. Despite the game stating that owning her and Mr. Fa-Sol-La-Si will cause their Power+ effect to only occur once per run, players have noted that the Power+ effect can occur twice, once for each pet owned. It is unknown why this occurs.
She loves to spend quiet nights, staring at the dark blue sky in absolute silence. She used to lament the fact that she could only produce a limited range of sounds, but now that she has Mr. Fa-Sol-La-Si by her side, they can both produce a harmoniously beautiful melody that is said to trigger feelings of love to anyone who listens to it.
Since the Season 5 update, the 'glitch' that causes the Power+ effect to occur twice in a run has been fixed. However, players have recently observed that this glitch is occurring again, and players are now able to obtain up to 4 Power+ effects per run.
Shortly after the release of Lime Cookie and Mr. Limeguard, there was another bug with Ms. Do-Re-Mi's Power+: She would pop up by herself 3 times each for the main Cookie and relay Cookie and Mr. Fa-Sol-La-Si did not show up at all. This has since been fixed.
In spite of the fact that the Star Firework Potions are considered a floating/winged jellies, they are still attractable by Magnetic Aura or Magnet Jelly.
Unlike her pair, she is generally used not for Coin Farming.
In 11 March 2016 update, the pet was buffed, requiring only 180 (instead of 500) to start producing the Star Firework Potion and gives higher energy recovery. However, at the maximum level, Ms. Do-Re-Mi will require 13 seconds instead of 10 seconds to generate the potion when you already have reached the stable amount of coins.
Currently in the LINE version, her Power+ works only when you obtained both pets. However, the effect can still be triggered twice per cookie, implying that the glitch has not been fixed yet. Also, the bear jellies are half-transparent, allowing the player to see part of the background.