Metronome is able to call Z-Moves and Max Moves.

I had been spamming Metronome against several wild Pokemon for 1 hour. During this time, Metronome called Max Wyrmwind, Clangorous Soulblaze, G-Max Hydrosnipe, Max Hailstorm, G-Max Meltdown, G-Max Terror, 10,000,000 Volt Thunderbolt, G-Max Rapid Flow, G-Max Finale, G-Max Cuddle, Max Airstream, Max Geyser, G-Max Snooze, Max Ooze, Max Darkness, Let's Snuggle Together, and Guardian of Alola.

Based on these results, it would appear that Metronome can call any Max move or G-Max move, as well as Z-Moves that are specific to one Pokemon. Metronome is not supposed to be able to call these moves.

Tested using The Pixelmon Modpack on CurseForge.

Hi there - thanks for your report! I was able to replicate the bug in the same way as you - using Metronome repeatedly in wild battles for some time, and ended up seeing both G-max Chi Strike and Decorate used, both of which are included on this list of Bulbapedia (https://bulbapedia.bulbagarden.net/wiki/Metronome_(move) ) for moves that shouldn't be called by Metronome.

As such, I'll pass this ticket onto the Internal tracker!
Cheers!
Katzyn