It's actually pretty easy for everyone to figure out who Mr. L is working with and why they took those four Avatars specifically thanks to the fact that GG has actually been playing "Connected Cosmos: The Game" and was looking forward to the new crossover update (her name is gamer girl, this is pretty much her Whole Thing, remember?). Of course, there's the issue that they can't just go into any old copy of the game and grab them once the update comes out, since it wouldn't be their version of them, so they have to find and break into the CCC's systems and the developer server, which is... shockingly well-hidden considering Jayin couldn't possibly know how to hide it from a Digital World perspective. Still, this is the internet, people talk, somebody's bound to know where it is. It also helps that, thanks to Timmy being so deeply entrenched in things and Alyssa obviously wanting to help when she finds out what's going on, the Grid is fully on board with helping the Admins and Meme Alliance in this, and Alyssa in particular has a lot of useful information to contribute as a co-founder and former employee of the company.
And of course there's plenty of friends they can call on from all over the 'net and beyond. Thus, the plan goes like this:
During prep we have three teams
Team one will scour the Digital Multiverse in search of an entry point to the Connected Cosmos Company Servers. Overseer and Abyssal will take point on this since Overseer has more knowledge of the modern DM's layout and cultures than just about anyone else and he already has Abyssal's contact info. The Grid will also be heavily involved in this part due to their extensive spy network.
Team two will learn all the ins and outs of Connected Cosmos: The Game so that when things get going the infiltration teams will have as much information as possible. Gamer Girl and the kids will be in charge of this since GG has a big head-start thanks to already playing it on her own time and the kids wanted to help and this was a relatively safe option for those of them who wouldn't have been as much help during the big fight.
Team three will be more general preparations. Getting the Codeship Fleet up and running, finding the cure for the Nintendo Firewall Virus plaguing the stolen Avatars, recruiting allies, coming up with the actual attack plan, etc. This will mainly be in the hands of the Avatars and the Meme Alliance.
Also, they need to transfer the memes refugees in Equestria to a server that can actually support a Meme Cycle as soon as possible, especially the Dead Memes. Discord is keeping them from becoming Corrupted somehow but whatever he's doing isn't sustainable in the long term, especially since it technically counts as actively preventing chaos and is thus taking a toll on him.
In the meantime, Jayin notices Tama is in the game when she's supposed to have been dead for years in-universe, but shrugs it off and figures she can just stick her in Devos as a random NPC, let the fans speculate, then come up with a quest involving her and put it in one of the smaller updates later down the line (it's an MMO, the players'll eat that shit up).
While Jayin's convinced she's already won (since her inability to see most Digital Beings as people means she's only considering Glitch Productions' possible reaction to this) Mr. L has enough experience both as part of Luigi and as the Crew's enemy to know this is far from over, so he slips through one of the leftover cracks between dimensions and makes a deal with someone those Junior Heroes would never expect...
Once things actually kick off, this is the plan:
The fleet, led by Peach and made up of everyone and everything they've got that can withstand Code Space, will battle the CCC's outer defenses (Twilight monsters, Brobots of every type, the CCC's own Code-level beings, and Mr. L's surprise guest who I'll be introducing in an actual ficlet) to keep the heat off of the infiltration teams.
One infiltration team will be all the Avatars/Anchors and their Crews and some other allies (except Doc and his Hamtor army, who have a Codeship and are part of the fleet) will enter Connected Cosmos: The Game courtesy of Timmy making a wish (since they know that FOP Fairy Magic trumps firewalls but Jayin doesn't), cure the stolen Avatars, then take out all the major Bosses in Renata, Harmonia and Sleeping Gaia (because the Twilit Rifts the bosses are connected to are acting as anchors keeping the stolen code attached to CC:TG's developer server) and await extraction.
The other infiltration team consists of Steve, Rob, Welony, Cursor, Samurai Bob, King Mickey, the AVA Squad and Enigmoth (the Paradox Pokemon, a legendary Bug/Dragon type that has Phase Shift, an ability that makes it not exist every other turn) sneak through the firewalls in a Gummi Ship using Enigmoth's Ability while Chroma and Blaze are being distracted by Mira (she's literally running across the physical firewalls to exploit the fact that firewall programs are programmed to destroy potential virus infiltrators at all costs because if you'll recall her base programming is to be annoying as hell and never get caught) so they can get into the maintenance areas of the CCC Servers and find and destroy the Purchase Keys so this can never happen again (Piracy, Bitches!!!)
Then the final steps are to breech the Firewalls entirely (they will, in fact, have several options for doing so) and have their strongest Programs grab the three Servers and the infiltration teams and hightail it out of there.
Jayin won't be able to do shit about it legally, since if she tries to press charges she'll have to explain how the hell it even happened, which will either make her sound nuts, or pull back the veil of secrecy and in the process reveal that she's exactly the kind of person she's been getting portrayed as in SMG4 and the Grid's videos when so far it's been seen by the viewers as part parody of studio execs in general, part Alyssa being understandably bitter about what happened to her. Either way her reputation would take a massive hit, and she would not be willing to do that to herself even if it would make her win overall.
As you might expect, this is going to work, but it will not go off without several hitches.