In this video guide I will show you how to play a group battle with two other players. First you will need to complete the tutorial towers. Then go into the towers of time, look at the top left, and one down to find the boss tower. It will be a timed event only available from time to time
. Once you select it to start looking for other players it should say group battle, Then you know you have the right tower. Otherwise it might just a regular tag-team match and that won't count. Once you find two other payers and the game loads up the achievement will pop.