As long as it’s not like the MVC2, with endless assists and infanites. I bet it would be like Bloody Roar… but not 3D of course. Sounds like a good idea though.
I say you cant have it all.
Make it a melee fighter without the ability to transform at will.
Certain specials, but mainly supers will feature them in Transformed states.
Ok, I’ve thought about a 2d TF fighter a lot myself, and here’s some ideas I have based on things brought up in the conversation thus far, thinking in terms of MvC2 style play:
Fighting
The point that TFs have mostly gun based battles is not necessarily true, as said, there have been lots of grappling and fist to fist style battles, not to mention a few melee weapons such as the Optimus energon axe, Megatron’s energon mace, and swords in the case of Springer, Blitzwing, Menasor/Motormaster, and the Dinobots, as well as Wreck Gar’s axe, and Hot Rod’s chainsaw as seen in the movie. The various construction parts of the Constructicons could be used as weapons as well, not to mention natural resources of offence such as Omega Supreme’s claw and the horns, talons, teeth, and claws of the dinobots and predacons.
You could limit projectiles to special moves and supers. For example, a simple hadoken command for Optimus would result in him pulling out his rifle HVB style and shooting off a few rounds, classic sound effect in tow. As for his hand to hand combat, alongside uppercuts, punches, kicks, throws, etc, he could have a command to summon his energon axe for a short amount of time, opening up extra comboing possibilities. One of Megatron’s specials could be an unused Decepticon character coming in to use him in gun mode temporarily, and he could use his fusion cannon in bot mode for a huge blast as a super combo. I could see a Fei Long/SF3 Yang style move for him with his energon mace, wherein you can pull off D,DF,F+P up to the three times as he uses the weapon. Starscream could use his null rays to temporarily make an opponent vulnerable, then dash in for a quick combo or a super where he transforms to jet mode, locks onto the character and sweeps across the screen whilst gunning them down.
Along with those three, there were a lot of different abilities given to many of the G1 characters, such as Ironhide’s glass gas, Skywarp’s teleporting, Prowl’s acid pellets, Hound’s holograms, Rumble/Frenzy’s piledrivers, Jazz’s sonic capabilties, and so on. All of these things could lead to plenty of variety between the fighting styles of the characters, meaning that there’d be more depth there than I think a lot of people are considering.
Combiner leaders such as Scrapper, Motormaster, Silverbolt, Hot Spot, or Razorclaw could summon their teams for supers where they either transform into their combined form for a physical or projectile attack, or even simply call them in for assists such as aerial raids from the aerial bots or dashing ground attacks from the Stunticons, characters likely to use their vehicle modes to crash into other cars. As mentioned before, group style attacks belonging to leaders of combiners could also go to characters such as Blaster and Soundwave, having the ability to summon their cassetes as assists in battle. Not only this, but you could have an Insecticon character call in the other two Insecticons, thousands of clones in tow for a screen drowning super combo.
Flight
Ok, so all the Decepticons can fly, yet only a few Autobots can. You could start by including a few Autobots that do have flight capabilities, such as Omega Supreme, the Dinobots, Silverbolt, Sideswipe(jetpack,) Springer, etc. Imagine hitting HP+HK, an Autobot such as Silverbolt or a character such as Starscream then flipping up into the air as they transform for “flight mode.” They can then fly around for run away or fly up to the top of the screen and then transform back to bot mode as they pull out their gun and rain down laserbeams upon the opponent. Some of the non-flying Autobot characters could simply have super jumps with different advantageous properties.
Transformation
Aside from the usefulness in flight for certain characters, there are other ways that the transformations of the characters could be used. For instance, you could have charging attacks where a character like Optimus or Motormaster temporarily transform into vehicle mode and ram the opponent. You could even have the ability to “run over” a character while in vehicle mode after they have fallen. Alternate modes could also lend themselves to certain moves such as massive projectile attacks from characters that transform into bases like Trypticon or Metroplex. You could also possibly put alternate/vehicle modes to use in dashes, with characters like Swoop transforming into pterodactyl mode and dashing across the screen akin to Jedah from Darkstalkers. Also, you can’t forget the character Six Shot, who had six different modes, all with different capabilities, such as a flying wolf that could no doubt be useful in battle somehow.
Character Upgrades
Besides the combiner characters forming with their team mates, you could also have max level supers that temporarily turn certain characters into their updated forms, such as Optimus into Powermaster Optimus, Megatron into Galvatron, Hot Rod into Rodimus, Cerebros into Fortress Maximus, and even Bumblebee into Goldbug. You could also have two upgrades from the Japanese series Headmasters: Blaster into Twincast, and Soundwave into Soundblaster. You could also possibly have Sky Lynx able to switch between lynx and dinobird modes ala style switching with Gen in SF Alpha, and have a super where the full combined mode is available.
Palette Swaps = Bigger Roster
Everyone knows that a company(i.e. Capcom) will do anything they can to cut some costs, and the roster of this game could get pretty large if the fact that so many TFs are basically the same robot/vehicle colored differently with slight differences were taken advantage of. All they would need to do would be animate a basic body in some cases(Prowl=Bluestreak, Starscream=Skywarp/Thundercracker, Ironhide=Ratchet, Inferno=Grapple, Trailbreaker=Hoist, Sideswipe=Red Alert, etc.) and make the slight aesthetic changes necessary to differentiate the characters from each other as seen in the G1 cartoon, and of course give them unique moves. This could really help beef up the roster if not done in an overly cheap way.
So really, there’s all kinds of things that could be put into a G1 TF fighter if someone were to really try. It’s too bad that unfortunately that probably won’t happen officially!
I like the idea of a game with 20 Sentinels.
Megatron cannon unblockable >
how about this:
Flight v Safe fall.
decepticons have flight, nothing can be done there.
the possibility of making the ‘flight’ be in the form of a second jump.
so they can jump twice in the air whereas autobots cannot.
decepticons also have float so they can drift in the air.
as well as air dash.
autobots cannot fly but get super jump and safe fall.
so they get a jump equal to 1.5 times the normal jump level.
and they can kk on landing and they transform into the vehicle version and take no fall damage.
and also can follow up ala A3 rolls.
Transformation
transforming is set aside for supers and assists.
for eg:
megatron - jumps out and tfs into a gun for the current fighter to have a blast with.
starscream - flies past for a strafing run that can guard break.
soundwave/jazz - jumps outs in stereo form to stun/dizzy the fighter.
optimus - drives past as a big rig and slams them against the corner and launches them.
grimlock - changes into a t-rex just like servbots super.
Shooting
the overheat would be the way to go.
big guns = less shots
small gun = more shots.
just a few ideas.
would make a mad ass game if made.
2d cel shade would be my bet.
like any game companies cbf drawing the frames needed.
Yeah, that would be major sweet to see something like that. In the pilot episode of the original Transformers, some of the TFs did some fancy hand-to-hand fighting attacks in More Than Meets The Eye. Some examples of what I want to see are: Mirage’s swing-from-under-the-skywalk-and-then-flip-in-midair-to-land-a-wicked-double-kick-on-some-Decepticons at that dam power plant or Prowl’s acrobatic ability as seen in that jet hanger bay when he was being remote PC-controlled by Chip or maybe even Jazz’s flying tackle (after being thrown) that you always see him do in the intro. 
Whoever thought of the Virtua On type of gameplay is dead on.
soooooooo many people just want to have the transforming and forget the rest of the gameplay thats why the last TF game sucked transforming needs to be used the same way they used it in the show to get around faster or escape (blaster/jazz and the dinobots are the exceptions)
Or mabe just call it Robots in Disguise and scrap the transforming all together.