As has been mentioned many times before, the best mode for getting this on is Cops and Robbers. However there's a twist to this new method, that makes boosting with a party much easier.
So long as you can end the game in a tie then it counts as a win for both teams. This is especially helpful if you manage to have a boosting party of 8 people as you don't have to take turns winning matches.
Solution confirmed by myself, Fox1278
, xX F0RD MAN Xx