The Heylin alliance arrived/Neighsay and the corrupt ones of Equestria joined in

Here is how the Heylin alliance arrived in Son of the Overlord.

Just as they were about to make plans, the Heylin alliance arrived.

Wuya: Mind if we cut in?

Gorog: Why are you here? What business do you have for trespassing our domain?

Heylin Chase Young: Just thought you could use some help for your revenge.

Gorog: We're listening.

Heylin Chase Young: We have other plans for our alliance to grow.

PandaBubba: And it require the help from all corrupt officials from Equestria.

Gladmane: That would be us.

Chancellor Neighsay: We were brought here by Heylin Chase.

Gorog: You're just the help we'll need along with the Sons of Garmadon.

Chancellor Neighsay: We too seek our revenge, Gorog. Whatever plan we'll follow, so be it.

The Overlord: Good, only my son and I will lead for our revenge!

Flim: Yes, I love the sound of that!

Flam: When do we start?

Gorog: We begin our evil plan at once!

Huya: That can be arranged.

Heylin Jack Spicer: Oh yeah! Let's do this!

So, they started to make plans for their revenge.