It's actually very simple too.
- Go into friendly kombat
- Pick Scorpion
- Go to the Subway stage (8-8-0|0-88)
- Perform Scorpion's "Pack" fatality (f-f-d-u-run)
- The game will glitch/reset and send you back to the main menu, and 2p will remain in the game.
- From there you can select 2 on 2 kombat or 8v8 tournament