Warning. This is not a tutorial nor it is short or visually explained.

I uploaded it as a memory. If you have ever beaten Terraria in Master Mode you might understand why I wanted to record this fight as a memory. (Also I beat Master Mode in multiplayer with my brother).

Anyway the video might be useful if you want to see a coop strategy in action. I'm sorry we didn't include my brother's point of view.

Basically we just took turns of taking Moonlord's aggro, ran for our lives (trough a very long skybridge) and hit Moonlord while running. When we were finishing running though the map's skybridge (or died) the other had to be prepared to take the aggro and repeat the process.

About the video:

My brother and I beating Moon Lord in Master Mode for the 1st Time.
Our strategy: A Tag Battle on a long skybridge.

Personal memory and a small contribution to Terraria's community.