Brightstar extends his Othersenses as well. He can 'read' the surroundings for almost a mile in all directions. What's showing up as magical? 

Near the top of a tall building about three-quarters of a mile north of where they are, there are two blindingly bright sources of magic, like the power of a thousand gods compressed into a point. One of those is probably what's responsible for the very-visible-to-natural-sight beam of blue energy that's shooting from the top of said building and creating a portal in the sky that the aliens are coming through.

About the same distance away, in the opposite direction, there are some more human-scale combat spells happening. However, one of the mages is carrying, but for some reason not using, a similar white-hot singularity of magic.

Tony swaps his time-travel suit for his combat one and follows Leareth.

"Alright. Space and Mind Stones are in that building"—he points out Stark Tower with the beam of blue energy coming from it. "As of right now, the government has decided to destroy this entire city in an attempt to contain the invasion. Past me decided hey, why don't we nuke the aliens instead, and is about to redirect the weapon through the portal. The battle ends very quickly once that happens. We need to be at Stark Tower when it does. We have about five minutes, which—I hope you have some method of transport faster than walking."

Strange Mindspeaks the group.

:Alright, I'm headed down to the Sanctum to talk the Ancient One into letting us borrow the Time Stone. I shouldn't need backup, but it won't hurt.:

Leareth glances at Nayoki. :You can do the Gate?: 

:Of course: 

She reaches out to slip into mind-rapport with Vanyel, sharing his Farsight. :We want that building: 

:Er, right: 

Vanyel's mage-gift is still in the re-training process after the incident at Urtho's Tower, by now he's basically fine with the 'giant fireballs' mode of mage-work, and they sorted out his allergy to Gates a while ago.

Which doesn't mean he likes them. He can handle it, though. He focuses his Farsight on a convenient point just outside Stark Tower. 

And Leareth turns back to Strange. 

:I can accompany you, if you wish. If the group at Stark Tower does need my help, I could be there in seconds, and - I confess that I am curious about the Ancient One. ...If you have a visual memory of the Sanctum or immediately outside, and do not mind sharing it with me, I can Gate us directly there: 

"Okay, we actually want to be near the top of the building, if you're making a portal," says Tony. "See the flat part that sticks out there? Also, it would be helpful if you could, like, make us invisible. Or at least make me not look like me, people will notice if there's two of me flying around.

"Also, if travel's instant, let's not go before the big blue beam goes away."

:You're welcome to come, but I'm perfectly capable of a portal by myself.: And he raises one, opening just outside the front door of the Sanctum.

Nayoki nods, wordlessly indicating for Vanyel to shift his viewpoint. 

:Illusions to make all of us truly invisible are difficult, but I can make us difficult to see, at least: 

:- I can do a backup illusion for just you: Brightstar tells Tony. :I can make you look like - my papa, I suppose: 

He knows Moondance's face very very well. Better than just about anyone else. Also he definitely has a lot of emotions about this, but they're...overall helpful emotions, for a mission where the entire purpose is revenge. 

Behind Nayoki's not-quite-invisibility blurring illusion, Tony now looks like Moondance. 

Nayoki concentrates, and raises a Gate to the flat sticking-out part of Stark Tower. 

And Leareth follows Strange through his portal. 

They step through Nayoki's portal, and out, invisibly, onto the helipad of Stark Tower, near the source of the blue energy beam. There's a woman there, jabbing at it with some kind of spear, which—when looked at through Othersenses—obviously contains the other Infinity Stone.

Great. We got both in one place. Can you, like, open a portal right below them? Past Nat will be confused as hell, but we can explain later.

:Directly under so that they fall through? Where do you want the other end?:

Yeah. Can you put the other end at the Avengers headquarters? The place where we were staying? At this point in time it was just an empty warehouse—I dunno if that messes up your portal magic—

Do it on my mark, as soon as she manages to stop the energy beam.

A few seconds later, 2012 Nat makes a final jab at the source of the beam, and it starts to power down.

Now.

For most mages this would be a problem! 

They traveled overland to New York from the headquarters before going back in time, though, so Nayoki knows the approximate bearing and distance, and she can anchor the Gate on 'this place, but now, still an empty warehouse'. 

It takes the search-spell longer than usual to stabilize on its destination, but the actual distance in miles isn't that far, for her, Within ten seconds a circular glowing ring appears directly under Nat and the now-powered-down source of the energy beam; it's about six feet across, big enough that she'll definitely fall through. 

The other side appears, also parallel to the ground, but at just-below-normal-ceiling hide, somewhere in the middle of the warehouse that would later be converted into the Avengers' headquarters.

Vanyel breathes out between his teeth, ordering his mind and body to stay relaxed, and keeps all of his Othersenses extended, watching for any hint of approaching threats. 

Alright. Can you do another one, upright, destination about twenty feet from the first? Also, drop the invisibility—and whatever's making me look like a Targaryen—I think I'll want to be recognizable for this.

:On it: 

Nayoki drops her half of the illusion with relief, it's very annoying to do complicated Gates at the same time, and snaps down the horizontal Gate before Nat can try to get back through - it'll be above her head, in the warehouse, but some people are stupidly good at jumping. 

She raises another Gate, still unscaffolded, but with the orientation and approximate shape of a normal door. Hopefully, 'there, but twenty feet north' isn't in the middle of a wall...

Aww, his illusion didn't even get to do anything. Brightstar quickly dismantles it, and heads through Nayoki's Gate first, mage-sight and Thoughtsensing on full alert. 

Natasha is very confused about why she just fell through a portal into a warehouse! She does have very well-trained combat reflexes, though, and she tucks and rolls out of the way of the falling machinery, then springs to her feet, gun in one hand and scepter in the other.

"What the fuck—Tony?!" she says when he comes through the second Gate.

Then she pauses a moment, reconsiders the situation.

"I don't know what tricks you're up to now, Loki, but it's over. You've lost."

Tony, just in case, closes his helmet over his face.

Guys, you're going to want some kind of physical shielding, just in case, he thinks at the mages. That thing in her hand can, ah, shoot metal projectiles very fast. Quite dangerous.

"I'm not Loki," he tells Nat. "We're from the future. 2018. Thanos—the guy who sent Loki—managed to get all six Stones. Wiped out half the universe. We need to borrow the Stones from this timeline to fight him and bring everybody back."