A game like this would require an advanced level of skill. Some things that you would need to do:
Create all the background graphics, create every frame of the character graphics for all characters, create all of the items, weapons, windows, effects, etc. Create all of the sounds and music. Place all of these graphics/animations in the right place at the right time. Provide collision with the background and with enemies. Track all of the characters' attributes. Create an online experience.
If you want to make something like this, you will need to invest the time and energy to learn how to do so. Real world: It's not gonna happen next week or next month.
You didn't say what software you were using or intended to use. You might want to look at PlayBasic. Whatever you use, start off with an easier project and continue to work on more advanced projects and develop your skills, realizing that it will take you a lot of time to get anywhere near this level. It can be a very rewarding and enjoyable (albeit sometimes frustrating) experience.
Good luck to you.
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