well not bad but,,,
theres alot of things that can be fixed:
1. mario cant "switch" between power ups because i saw him go to fireflower 3 times so lose that
2. you should just have him use 1 power up at a time & some time betwwen when he loses one then uses the next
3. yeah i believe goku should go super sayan near the end & mario should combine his star & feather together so he could "power up" or go super sayan luke goku if you wish
4. you could improve the qality on the landscape when close up
5. also just as there facing off you should have 2 buttons that allow people to choose who wins
6. also you could add alternate ending buttons ass well so luigi comes in & kiks goku in the nuts from behind & then they double team on him or krillen comes in & blasts mario just as mario is gonna kill goku
7. maybe add a backstory (short) off how there fates intertwined, like goku could off been framed for killing peach & mario then trakcs him down to your choice of landscape
over all you have a good concept just need to improve