Prepare yourself for the most difficult achievement Injustice has to offer. These S.T.A.R. Lab Missions replace the infamous Challenge Tower from Mortal Kombat. The great thing about these Missions is that they include one on one fighting between the characters and ridiculously entertaining mini-games like dodging lasers and guard lights in a museum while playing as Catwoman's pet cat, Isis. The not so great thing...is that there are 240 Missions and you must complete them perfectly for this achievement.
There as 10 Missions for each character in the game. Each Mission has three certain requirements that must be completed in order to obtain the stars for that Mission. In total, there are 720 stars that must be collected.
The upside to this, is that the three stars do not need to be collected all at once. You can work on one star at a time if that makes it easier for you.
During the Mission, you can pause the game in order to see what your star requirements are. For example, in the first Mission while playing as Superman, the requirements are:
Strengthen your skills
Land a 5 Hits Combo
Execute a Combo greater than 30%
When you complete a requirement, you will obtain a star. While this first mission basically hands out the stars, the missions and their star requirements will get harder right from the start.
Unfortunately, you cannot pick and choose out of order which Mission you would like to play. The later Missions will only unlock once you have the required amount of stars needed for them.
If you need help understanding any useful tips and tactics for certain missions, you can check out the links below:
S.T.A.R. Lab Missions Guide - Videos
S.T.A.R. Lab Missions Discussion - Tips, Tricks, & Tactics