When it starts out I kind of can't recognize it but as time goes on I recognize it as the underwater theme that would play while under the water. Funny how the only way to get the Regis was to go underwater and find that super secret cavern of theirs.
The xylophone at the start that plays the whole time gives a water feel as if you were underwater while listening to this. The synth has a nice crystal sound effect to it which feels very relaxing to me. The chorus and bass line come together and make it feel like it could be the last time you go there underwater.
The tune really captures the curiosity of what lurks under the surface. At the same time part of the underwater theme kind of sound like a remix of the Lavender Town theme, how strange.
Overall, beautiful cover.