[mrcactu5]

if all I want to to is build a Super Mario clone is the knowledge of the 6502 assembly language still necessary ?

[monocasa]

It'd be helpful, but not strictly necessary.

Here's an extremely well commented disassembly of Super Mario Bros.

https://gist.github.com/1wErt3r/4048722

[saagarjha]

No, you can just make it in your language of choice. If you'd like to emulate it then you'll probably need to learn it.