WWE 2K20

To unlock this achievement, you will need to create a MITB briefcase, win it in a PLAY mode match and then cash it in to win a championship in another PLAY mode match. Both against the AI, as the description suggests.


MITB: Creations -> MITB -> New. Here, you can create your briefcase. Select the championship you want to win and give it to the superstar you want to give the briefcase to. In my case, I simply left it on the Universal Championship and left it vacant.

To make matches end a lot faster, go into the match settings before selecting the superstars and set health to low and automatically give the wrestlers 1 or 2 finishers. Make sure you accept this after changing the settings. (Thanks to GingerAmongUs and Dreams Repeat Gaming).

Winning the briefcase: Play -> One on One -> preferred match type. Select who you want to win the MITB briefcase, I chose Tyler Bate, and simply win the match to set you up for the cash in. To put the MITB on the line, simply click the and select the MITB option before selecting your created MITB briefcase.

Cashing-in: Play -> One on One -> preferred match type (not the "backstage brawl" or "brawls" types). Select your briefcase holder and the Universal Champion (ie Tyler Bate vs Seth Rollins if he's your champion) and make it a title match by clicking the in. Select championship and then Universal Championship *confirm with * and it should give you a pop-up message about cashing in the briefcase, you want to say "YES" to this.
Win the championship belt and the achievement should pop.

Edit* Changed the solution to match the most common method of unlocking the achievement. It appears to be glitchy regardless of the method used, but winning it before cashing-in is more reliable than assigning it to a superstar.

Edit 2* added health point.