According to OP:
"
This MUGEN project now in IKEMEN-GO still in development, which started to be developed in 2018, the best jus chars from the best authors , all the characters were balanced, improved and standardized the commands.
WHAT IS THE PROPOSAL OF THE GAME?

Has unique upgrades like Wendy's DragonForce, Sting with WhiteDrive, Hidan's Circle System, etc.

All have the same commands for transform, fatal and skills.

All fatals have a chance to react, defending or dodging (depends on the fatal).

Some abilities have cooldown, like fired projectiles.

Common transformations are more fluid and can be interrupted, if you win the fight you remain transformed and return to base form if you are knocked out.

Some characters have "Secret Transformation", which can happen when they are low on health (Ultra Instinct, Kyuubi, Nightmare Luffy, Gear 5, Ichigo Vasto Lord, Hyper Sonic, Meliodas Demon form, etc )

Has secret characters; boss, minigame, etc.

SHOP system (collect stars by playing to summon characters, stages and modes).

Original Story Mode.
And more!

Seal System: Seal users detransform the enemy (Piccolo, Sai, Pain, etc)

Logia System: Elemental users temporarily transform into their element with a high chance of not receiving damage in exchange for energy and improves some skills (Ace, Enel, Crocodile, Kizaru, Suigetsu)

Haki System: Moves that contain Armament Haki hit Logia forms 100%.

Improved stick commands for all characters (Ex: Hold Start + --> + a)
"
Note: this recent version is free and I have provided a direct link but, if you want all the characters + stages unlocked it's behind a paywall on their ko-fi so classic using assets that aren't theirs for money (something that we are highly against). I wouldn't recommend seeking any more of their things entirely. when there's other large and cool anime mugens out there that is for free and doesn't require $3 to unlock all the characters and stages.