Obviously this achievement is gonna take a long time and a bit of skill. However, its actually a easy achievement. I am gonna give you some easy tips on how to do these. Just be happy these are MUCH MUCH easier than the challenge tower in MK9. Most of them are very repetitive.
Firstly, everyone knows that you do not have to do all 3 stars in one try. However, you must complete the objective for the star you got to be counted. So, just take your time and do 1, 2 or 3 all the same time if you can. Some will actually need you to play the challenge more than once anyway.
Secondly, for those who have problems with the difficulty. You will be pleased to know that this is just like MK9. The more you retry, the easier it gets. So if you are having trouble beating some one, just keep retrying, it will get easier. You must get to the mission unsucessful screen and try again. Not pause and select retry. It may take up to 20+ retries for noticable difference but it will get easier, dont fret.
Thirdly, for QTEs. If you are not fast enough to enter the button config. Push pause once the QTE comes up, you can still see the buttons that need pushing, unpause and do the action and push pause again for the next one and so on and so on.
Fourth, for challenges that ask you not to get hit for certain amount of time. Remember, you CAN block and it will still count. Spam projectiles from far away if you have them. If not, make use of super moves, interactables, throws and transitions. Those will eat up the seconds. A good tip is to build up a few seconds by running and keeping away and then use a supermove or transition for the rest.
Fifth, for juggle and combos challenges. Most of them are simple ones. For the rest, just refer to youtube, there are many vids that show you good combos for each fighter. Link to a uploader at the bottom. Don't forget that adding a meteor burn (RT) will net you a few more hits. ie. Green lantern's machine gun and nightwing's spinning batons. Experiment with it.
Sixth, for button mashing challenges like Flash racing superman. Obvioulsy, if you have a turbo stick, these are non issues. However, if you don't. You can use the spoon trick. It sounds weird but if you use a spoon to mash the buttons, you will find it better than using your fingers.
Seventh, it is very important to note that some of challenges are based on luck (trial and error). ie. Challenge 99: Lex Luther. Sometimes the air bubbles and bombs will be in great positions, sometimes they won't. Just keep retrying until you get lucky and all the air bubbles or bombs are in the right places for you.
Eigth, by far the hardest callenges are the ones that need you to have a full second life bar. My advice is to keep re-trying to make it easier and spam the projectiles from far way like crazy.
Ninth, there are some challenges that will require you to mash the BACK button to see where the next object is coming from. Examples of these are: Cyborg#126, Deathstroke#77, Lex #98 and so on and so on. If you mash the BACK button, you will have extra reaction time to figure out what your next move is and where to hit or go. You will definitely need this trick for hawkgirl's challenge. Dodging all the rocks without getting hit. Just spam the back button and move hawkgirl out of the way. Like slo motion haha.
Tenth, for win a clash challenges. I found it easier to quickly get myself up to full super. The AI will have full super sometime during the fight. Get the AI to use his supermove or a meter burn. You must have more and bet more super than the AI for guaranteed win.
The AI will almost always intiate a clash but if he doesn't, you can easily start one. Just remember, Clashes can only be intiated on the second life bar.
Eleven, Some of the 1st challenge for each character will have your doing all their moveset. Some of these challenges require you not to miss a move. However, this is very decieving. You probably did them all but did not get the star right? That's because you must hit the AI with the move, if he blocks or jumps out of the way, it wil not count. It might register, but it will not count for the star. Also, if you at anytime you hit air with any other move (even single punches or kicks), it will not count also. You have to hit and connect on the first try flawlessly and cannot do any other moves. Just take your time and do each move slowly and correctly. One particular nasty one is Black Adam. He has 3 combos you must get perfect timing. Also, you must hit sinestro with your lightining bomb on the first try. This is easier said than done. Throw a CLOSE one (it'll still count) Down Back +Y+ Back. It will land under him. Some times it will hit him, sometimes he wil jump away. If you miss, you have to start all the way from the beginning. Keep trying, you can do it.
Twelve. By far the hardest challenge in the game is Black Adam's #220. You fight 2 guys and you have to get hit by a super move and win, all while ice is falling on your head!. My advice is to kill killer frost as fast as posible and have at least more than one full bar of life. Beat up Shazam, . If he is on his last bar, do not combo him or he will clash you. Just jump around until he does his super and hit him with cheap jabs and kicks. he will eventually do his super. You must let it hit. Then quickly kill him. Make good use of he interactibles, your character power (B) and your super move to kill Shazam fast. Remember, keep retrying if you fail. 15-20 times and you will see a big difference in the difficulty. Do not ever pause and retry, you will reset the counter.
If you have any problems with a challenge, leave them in the comments and I will try to help you. I will edit this and add more tips as I go through the star labs myself.
IE, a lot of people had problem with Superman's vs Batman trying not toget hit by his batrangs. You CAN block and still get it. Just stay far away from him (full screen) and spam superman's projectiles. Down Back+A, I believe. Time it so that as he gets up, you nail him. He rarely blocks it. if he does, just hit him again. Try not to jump so much or risk getting hit from his upward batrangs.
Most importantly, be patient. Dont rage or get mad. If you are having problems with one, move on to the next and come back to it later. Take a break if you need to. You will find that if you come back to it, you will be much better at it. Have fun with these star labs. A lot of them are so much fun to play.
Still having problems. Here are Vids to guide you. I am not going to post every single fighters vids here. The uploaded named VesperAzure did them all. Just go to his channel, look for the fighter and challenge you want and copy it.