hey I really like your project if you take feedback I have some suggestion take them like you want. (mostly balancing even if it is just for fun)
I think that contra guy would need just a little more hp maby like 5 bars
The mega mans should have something else than tracking missiles and let that to the contra guy exclusively. since they got a lot of hp they are already very strong!
Samus and link could have a little more hp and samus could get screw attack and a reserve tank in power ups similar to link's fairy
Can sonic trio have a little more power ups or is there nothing else in their games?
I would be cool to see bowser HP
Maby luigi can get his smash fireballs?
Mario look very strong a possibility to nerf him a little is when he is small and takes a power ups it would act as a normal mushroom.
can youu put the timer visible before the sudden death and are stock battles/tag battle a possibility?
thx for the reading I hope the best for this project