It certainly took me long enough (it's my first one after all), but I'm finally done with my take on Forge's mod!

Download link:
https://www.mediafire.com/file/hy3i2p23l3gv5ig/Forge_by_Nicaras_v1.5.zip/fileOptional--an alternate mannequin using Forge's 2nd skin (the Ultimate one).
Download link:
https://www.mediafire.com/file/o2gfj7d87idwdlx/Forge_PS2_XML2_mannequin_v2.0_by_Nicaras.zip/file
CHANGELOG: This
1.5 version is probably my last update on Forge. It brings another long-due fix, discarding his now unnecessary moveset_forge_flying file entirely (which affected his herostat entry) and moving some of its lines to his powerstyles file in respect to our efforts to stay within the game's limitations. It also brings some pretty much needed script files from Outsider's Mystique mod, so his Holographic Transmitter is finally working as it should (I only noticed it wasn't when I replaced Mystique on my herostat for Synch, so the script files went missing and Forge's power stopped working). Now this power is alright once and for all.
1.4 version brought a long-needed fix on Forge's powers with guns, as they occasionally didn't "vanish" from his hand at the end of the power.
1.3 version adjusted one small detail on the projectile of Forge's 1st power (which means I only tinkered with his entities file this time around).
1.2 version added a new idle animation, extracted from Forge's XML2 NPC. It also added better starter and finisher power combo texts (the names are making much more sense now). Also his 3rd power was not showing any longer the icon that asks the player to keep on pressing the power button. Finally, it turns his first skin back to its original size, like Julio Cabral has intended to.
1.1 version adjusted the EP cost of one of Forge's powers, the Stunner Grenade (and my thanks go to Bingerz for pointing that out to me in the first place). It also gave me the opportunity to re-check the whole talents file and re-write a few stuff from the descriptions. Finally, one other major adjustment I've made was making it possible for the Geo-Thermal .960 to be used during flight without the strafing chaining (which really doesn't make sense in the air). It'd be amazing if Forge could glide while shooting his blaster, but we don't have that kind of animation (yet), so this is where I'm standing with this mod today.
To properly run this mod, you need to copy all of its folders and paste them inside the main folder where your game is installed.
Then, you need to decompile your herostat.engb using the XMLBCUI software and edit it, replacing one of the characters from your current roster with Forge (simply copy all lines from herostat_forge.txt and paste them inside the recently decompiled herostat.xml, replacing the lines of the character that's going to leave your roster). Don't forget to get its menulocation number and to give it to Forge. Now you need to compile the herostat.xml back to the .engb extension and copy/paste it back inside its proper folder.
Optional: download the x_voice file from
http://www.mediafire.com/file/tumqqfxvewyxww1/x_voice_9-20-2014.rar/file if you wish to have Forge's callout line, among others. If you also wish to give Forge its "break" line (that's when he would say something before leaving the character selection screen and entering the stage), you have to edit this same x_voice file using the Zsm Editor software (or Zsnd). After installing that software, use it to open the x_voice file and then add the "forge_break.wav" file (it's inside my mod's main folder) following
this tutorial.
Now you should be ready to fully play with it.
P.S.: These four skins have each their own body proportions (each one comes from a different game) so much that sometimes I had to make them a separate bolton, or set different values to achieve the correct bolton/effect positions and avoid clipping. Therefore I'd strongly advise against replacing any of his skins without thorough gameplay testing and editing the powerstyles file to adjustments. So far Forge doesn't have more skins than this mod is offering, but hopefully in the future we may come across new outfits for him, in which case I can totally work out on solutions to adapt the powerstyles coding.
Credits and Acknowledgements:Skin 23001 - Classic (Marvel Heroes) skin by Julio Cabral (3D model adapted from
Xelandis)
Skin 23002 - Ultimate skin from Nodoubt's XML2 PS2 pack
Skin 23003 - Modern skin by BLaw
Skin 23004 - Astonishing (X-Men: Destiny) skin ripped and rigged by ak2yny
Mannequin (Classic Skin with Geo-Thermal .960) by Julio Cabral
All HUDs: Nicaras
All icons: Nicaras (extracted images from the X-Men comics)
Loading screen: Nicaras (original art from Julie Bell)
Scouter bolton: Nicaras (3D model from
100 Seedless Penguins)
Containment Gun bolton: Nicaras (adapted from
CGTrader)
Electric Blaster bolton: Nicaras (adapted from
CGTrader)
Geo-Thermal .960 bolton: Nicaras (adapted from
Sketchfab)
Rocket Pods bolton: Nicaras (adapted from
Free3D)
Shield bolton: Nicaras (adapted from a
Turbo Squid model, I think)
Voice lines: Nicaras (extracted from the "X-Men: Destiny" game with the amazing help of ak2yny, voice acting by Phil LaMarr)
Callout line: Ceamonks890
Upgradable Knockback: coding idea adapted from Outsider' upgradable Grab Smash
Holographic Transmitter script: adapted from the Infiltrate script (Outsider's Mystique)
Infiltrate powerstyle coding lines: adapted from Outsider's Mystique power
Humanoid team switching power: adapted from Outsider's Phil Coulson nonhumanoid stunning filter
THANKS A LOT, EVERYONE! MISSION ACCOMPLISHED!
Special thanks go to Outsider, BaconWizard17, UltraMegaMagnus, Julio Cabral, and ak2yny, for all of your help and instructions, and also everyone in this community who has provided us with the tools and the knowledge to make these mods possible.
Congratulations! Looks like all that hard work has paid off 
Thanks a lot, Ceamonks! I hope you all enjoy playing with him. But please let me know if any bugs come up.
I forgot to mention, but this mod's got a few cool tricks you'll find out during gameplay.
Also, I think it's worth mentioning that I've got most of the ideas for his inventions from the comics (and the
https://uncannyxmen.net/node/5832/page/0/9 webpage had them all listed out so it was really helpful). His Electric Blaster, though, was based on one of his moves from the X-Men Mutant Academy 2 game.
What else? I tried my best to make this mod original even if only for a single little detail, so his animations and coding lines are a mix from several other characters, as well as his power effects, which have been altered in color, size, or overall aspect, whenever possible. His Xtreme power (based on Mr. Fantastic's Orbital Attack) originally "missed" a hologram panel on his hand (we don't even realize it because of the size of his hand), so I had to make Forge one. I'm afraid I just won't really be able to tell the exact logic behind it because it was a very trial-and-error process, it took me a very long time altering the values back and forth to spin, resize and move it all around without knowing exactly what would happen each time, and I stopped as soon as the panel looked slightly satisfactory (or else I'd still be trying to get the perfect position and shape of it).
Oh, also I've developed this mod using the 50 roster hack, but I believe (and hope) it works on all versions.