A game where you have fully customizable female playable characters and the devs were like "yeah we were gonna add male playable characters too, but it wasn't in our budget"
EDIT: wait I forgot about skullgirls, which is mostly this.
More fighting games with absurd levels of customization. Skullgirls showed that we can push a not-really-palette system to give us unique designs out of a 2D fighter. What if we took systems from all kinds of games and amalgated them? Such as the SNK v. Capcom 2 Grooves, and the Arcana Heart alignment/goddesses, throw in Under Night In-Birth's moon phases- these three together are already a pretty absurd level of customization, and now assume that they affect the look of a character.
Tackling each one in reverse order:
UNiB moon phases:
Full Moon heavily reduces combo options and has rigid light->medium->heavy structure, characters feel very "heavy", damage is boosted and reaching maximum meter allows for a short install period where some health is regained. Can charge super meter.
Half Moon gives an almost uncontrolled light feel, with lower meter and slow regain of HP during the timer as well as an automatic burst. Relies more on comboing for damage, has little in the way of defensive systems but regular guarding is more resilient.
Crescent Moon gives the user a great amount of freedom with their meter, allowing it to be activated early at lower amounts of meter, waiting for maximum gives longer and stronger effects. Most versatile of the three.
Arcana Heart arcana system:
Characters have internal special moves which are augmented by Arcana specials, depending on which Arcana is taken. Each one is also supplemented with different features, such as negating chip damage, making charged moves unblockable, add meter drain to fully charged attacks, etc.
SNK vs Capcom 2's Groove System:
This changed the way a character handled entirely, altering the gauge itself and the subsystems a character could use. Being able to parry or evade, run or dash, hop, superjump, air movement options- it was all tied to the Groove, as well as the Meter. Only one meter allowed use of Level 2 supers, the rest only allowing for Lv1 and Lv3s. K-Groove, aka the Rage Gauge, only increased when taking damage, but a character could block at precisely the same time an attack would hit for a small regen and extra gauge.
The systems don't play nice with each other at first, though can be tinkered with and made to fit. The Moon system most heavily affects base damage and ability to chain attacks, the Arcana system most heavily grants new sets of attacks as well as adding some sort of features, where the Groove System most heavily affects movement options and the meter's inner workings.
Let's say you've got a base character, someone pretty simple. Easy to pick up, and such. Let's use Fillia from Skullgirls- mostly a rushdown, a little bit of range on her specials and supers. Under the Moon system, you'd probably want to avoid Full Moon, as the other two styles can easily play to a rushdown character... but what if you did take Full Moon? Some specials would change- as the Moon System can alter internal moves- to accommodate, combos now being shorter and harder to put together, Ringlet Spike now changes in power instead of distance and automatically hits under the opponent, the Heavy version doing multiple hits but not being comboable off of, the L or M versions can.
Secondly, the choice of an Arcana- lets say we've taken Full Moon Fillia, which can already be seen as sub-optimal, however, the Arcana can help sway us in a new direction even more. Arcana specials use their own button so they don't interfere with internal specials, so let's take Magnetism. Arcana specials have magnetic pull, we fall to the ground faster than others, and our forward Heavy has a hard pull, allowing us to yank an opponent in. Unfortunately for us, the Full Moon won't let us back off of the Heavy, so we'll have to use a special or a super at that point- still, it's a great way to stop an opponent from guarding a dry super.
Whenever we install (All systems play into this, the Arcana controls the actual input) we gain constant magnetism pull (and through Full Moon) regain health immediately from our Red bar.
We gain two ranged specials, one being a strongly homing orb and another being a random object throw. Our supers generate a damaging magnetic field with constant and fairly powerful magnetism, at least forcing some chip damage, and another random object throw this time launching four at different angles, allowing for a good zoning tool. A Level 3 super, a gravity well attracting both characters to the center of the stage appears and is bombarded by the orb projectiles.
Lastly, we'll need a Groove. Now, the Groove System is what needs the most editing to fit here, especially since I'm tempted to throw out Lv2 supers in general (as all of them have to come from the character already.) S-Groove will help us out here, as we get dodging and counterattacks for up-close, as well as chargeable supers and free lv1 supers at low HP.
Lastly, we must look at the Install. Our groove does not affect this at all (pre-tinkering around, I think only K-Gauge affects install), however, our Full Moon gives us an instant HP boost when it's activated, and can be activated out of any normal or special that can be cancelled, also has a burst option during install. Our Arcana gives us a constant magnetism during the install. Our Groove allowed us to install at 100% or one bar, the equivalent of a level 1 super. This would normally reduce the effectiveness, but it simply gives us less time to work- this is fine, since HP regen is instant and the only lasting effect is magnetism and the chance to burst.
The myriad combinations all result in a different playstyle- from the very beginning we broke down the rushdown-and-combo aspect of Fillia and exchanged it for raw power, magnetism, and subsystems to allow for fast switching between defense and offense.