According to my understanding, the ending theme song in the soundtrack of the movie "The Meg 2: The Abyss" was composed by film score composer Harry Gregson-Williams , the track is titled "Way Down We Go."

This song was originally sung by the Icelandic band Kaleo and was first released on the 2015 album "A/B". It was used in the ending credits of the movie The Meg: The Abyss and in the movie trailer.

Please note that movies may be released in different regions and versions, so there may be different musical compositions in some countries or specific versions. If you want accurate version information, I recommend checking the film's official music publication or contacting the film's official channels for more accurate information.