When i was in wal mart i saw a bottle of Marine 2 cycle, so my question is...

Is it Necessary to use Marine 2 cycle on a 2 cycle outboard?

What is the difference between Marine 2 cycle and regular 2 cycle?

Thanks

Regular two stroke oil is for air cooled engines and marine two stroke oil is for water cooled engines.  That's why the marine oil is TCW, the W stands for water cooled, you should not mix the two.

Even in TCW-3 oils, not all are equal, cheap oils are cheap for a reason, they don't have additives to prevent wear and carbon the better oils have.