Skulltag Invasion Custom Monster Spawn

[TendaMonsta]

What exactly do I need to do in order to have a "map spot" spawn a custom monster and have the same type of options as an invasion monster?

I would like to add some random monsters to my first invasion set and I don't exactly know how.

[Gez]

Use a random spawner.

[Mithran Denizen]

It's all explained adequately here on the ZDoom wiki.