The first idea Jack had to prevent this was to find the Tesseract, but he couldn't because Fury had hidden it well. The second idea was that as soon as Loki stole the Tesseract, Jack would use the system to track it down and steal it back from Loki.
The third idea was to stop Clint from attacking the Helicarrier. That was one of the reasons why Jack brought Bruce to the lab, so Nick couldn't find him. But because Jack was in the Negative Zone, he couldn't do any of this.
"We have to find that Tesseract. I have a bad feeling about this. Once you put on your superhero suit, try to find it. I'll try too," said Jack.
"Alright, I'll try to find it. For you who've never seen it, it's a blue energy cube. It's hard to miss if you see it," said Peter, and left the restaurant.
Jack also left the restaurant and went to Stark Tower just to make sure that Loki wasn't already planning to open the portal. As he was thinking about this and looking at the Stark Tower, a blue beam of light shot out from the tower and into the sky, and the sky opened up.
Jack saw a space tunnel opening up in the sky, and he knew that the Chitauri army was coming. Chitauri soldiers descended on something that looked like a flying motorcycle, and all the people of New York looked up to see it.
"Peter put on your suit and go to Stark Tower. There's an alien army coming to attack New York. I'll go there and try to stop them," said Jack, and flew off.
He transformed into Battle Sage and went to Stark Tower. As he got close, he saw Tony flying and Loki lying on the ground, with Dr. Erik Selvig unconscious beside him. Tony looked at him in shock for a moment.
"Are you alive?" said Tony, shocked.
"I think so. Let's talk about it later. I need more armor. This alien army seems too big for us to handle. The armor I have is a little damaged, with no weapons and no energy," said Jack.
Sure, I made many armors like you said we might need, it seemed like you were right, you use your clones and control as many as you can, I'll let J.A.R.V.I.S control them, my armors are at my mansion in Malibu," said Tony.
"Okay, let's deal with the first wave of aliens and then I'll open a portal to Malibu, then your army of Iron Man will appear to the world for the first time," said Jack.
"Okay, we have some new hero friends, they can help when they get here," said Tony.
"I know Spider Man, was talking to him when the portal opened, he's nearby, I'll deal with the big ships that look like monsters, call the government to urgently evacuate nearby streets," said Jack.
"Tell them to send people to the subways and for the police to focus on getting people out of the buildings, whoever can't move to the subways, gather them on a street where I'll create a portal and take them away from here," said Jack.
"Okay, I'll do that," said Tony as he fired.
The two were talking while destroying the aliens that came out of the portal, Jack was waiting for the right moment to destroy the first Leviathan, which was the giant Chitauri ship that looked like a monster.
Jack activated the Raiton Chakura Mōdo and flew at maximum speed towards the Leviathan, he went in front of the monster and entered through its mouth, and released lightning from his body while punching the air using his strength and soon used Chakra in his hand and created a sword and opened the Leviathan from the inside and left, leaving the first Leviathan destroyed.
This was the fastest way for him to kill these Leviathans without destroying New York and Jack wouldn't get dirty because the Chakra protected his body, Jack went out and started releasing lightning from his hands, this was a mixture of Chakra with magic that was not the same as he learned in Kamar-Taj.
"Nice, you easily killed that monster. I thought we would need Thor here, but you are smarter than him and also know how to use lightning," Tony joked.
Soon Thor descended from the sky just as Tony finished talking about him. Thor went straight to the Stark Tower to talk and start fighting Loki. Jack saw the scepter in Loki's hands and planned to wait to grab it later.
Then Jack heard Tony talking with the other Avengers, who said they had arrived and parked the plane near the Stark Tower. Jack then saw Spider-Man arriving and attacking some Chitauri army aliens.
"Spider, try to kill as many aliens as possible. Remember, they are monsters invading Earth and just want to massacre all humans. Just kill them and have no mercy, otherwise, more innocent people will die," Jack said.
"Ok, Battle Sage, I will deal with them. Has the Fantastic Four shown up yet?" Peter asked curiously.
"Not yet. If they take too long, there won't be much time left for them to fight. I'll close the portal after killing some aliens and as soon as the brothers finish talking," Jack replied.
As soon as Jack finished saying that, he saw Human Torch flying in the sky and making the iconic number 4 with his flames. Human Torch then flew closer to Jack and saw everything that was happening.
"Hey, Battle Sage, we have a battle right after arriving on Earth. I really don't know what the other heroes would do without us," Johnny laughed.
"This hero's life is really tough. Hold things up here in the sky with Spider-Man. I have to get some new armor. Those are too old," Jack said, flying next to Tony and opening a portal to his mansion in Malibu.
Tony knew what to do and followed Jack to the other side. Tony quickly arrived at his mansion and asked J.A.R.V.I.S. to activate the armor. After a while, Jack and Tony saw more than 150 armors flying. It seemed like Tony had really made a lot of them.
"Jack, you can take as many as you want for today. It's not Christmas yet, but this is my gift to the aliens. It's a good thing you told us to make so many of them," Tony said.
"I'll leave the armors you gave me here for you to fix later," Jack said, taking out the 12 armors from his spatial storage. Tony was shocked to see how broken they were in several parts and without any energy.
One more extra because it took me a while to post and thanks for the many Power Stones.
I had Peter summarize a lot of the movie with him talking about what he saw.