Here's how Ernie's army is gather and his betrayal to the Human Mane 6 in Ernie the Dragon Hunter.
[We see Ernie's army gathering weapons as we see him on his ship watching]
Sideshow Bob: Ernie is a fool. I should be a new leader and take his place.
Charles: Traitor! Ernie is a great leader, he'll never be overthrown....
Human Rarity: We get it, blah, blah, blah.
R2: What you may not know Rarity, is that one of those dragon riders is a equine version of you.
Human Rarity: Don't sweat it, droid face.
R2: My name is "R2-Q5", sweetheart! Because that's the last thing before I express my feelings with a song. [singy-song] "The itsy bitsy spider....
Michael: AH!! I DON'T WANNA HEAR IT!!!!
[Everyone starts arguing]
Ernie: [slams his staff as everyone stops] Sideshow Bob, my plans are for power! Not domination!
Sideshow Bob: [chuckles] My bad, my league.
Ernie: Just making clear. Once we head to Equestria, we'll terminate King Solar Flare and his daughters will be next!
Human Rainbow: And we'll rule the world!
Ernie: Who said anythig about that?
Human Pinkie: I thought you did.
["Meeting Drago" starts playing]
Ernie: You'd helped me destroyed Quahog, you helped me get enough dragon hunters for my army! And now, you are useless to me.
Human Rarity: What?
Ernie: Men, togteher! We destroy King Solar Flare with his daughters!
Ernie: Charles, look them up.
Charles: Yes sir! [grabs them]
Human Applejack: Hey! Let us go! Ya' won't get away with this Ernie!
Ernie: I already did. Ready the ships!