**** IMPORTANT ****
The DLC cannot be downloaded anymore.
But you only need two people with dlc to start the cat and mouse open event.
AS LONG AS the 3rd and 4th player are local guests to either of those 2.
So, ONLY IF YOU TRUST another player who has the dlc with your access details,
he can get the achievement for you.
*** ONLY IF YOU FULLY TRUST ***
Consequences of giving your account details can be pretty serious,
so do not blame me if it happens.