As you should know by now there are two routes to getting this achievement, defeat the Magneto missions and complete a 3 ball wizard mode or beat the 3 side missions and defeat a different 3 ball wizard mode twice.
Without going into the why's and wherefores I'd strongly suggest the side missions as they are easy to complete and the 3 ball wizard mode involves hitting just 7 ramps then the unite ramp to defeat the sentinel. Once defeated you get a chance to defeat another sentinel although should you fail you can simply beat the 3 side missions again and try for the 2nd sentinel.
Blob - 4 or 5 shots up the nightcrawler orbit will activate the mission. You then need to hit for shots and get 20 seconds for each shot. The ball will be delivered to the correct flipper for each shot to make this easier. The order is always, Cyclops, Iceman, Storm and Unite.
Juggernaut - 4 shots up the Iceman ramp. you then need to hit the Iceman ramp a further 3 times, you get 30 seconds for the first shot and a point countdown for the next two, which could be as long as 60 seconds. Just hit the unite ramp and Iceman ramps alternately and this one is easy.
Mystique - 4 shots up Wolverine orbit to start this mode. you then need to find Mystique. To make life easier the mode starts with the ball set to the top right flipper giving you an easy shot to the Cyclops orbit, which in turn delivers the ball to the top left flipper for a shot at the storm orbit. Mystique can be hidden on any of the ramps or orbits, although a successful shot up the Wolverine ramp will show you which ramp/orbit she hides in.
After beating any mission the Lock is lit on the Wolverine orbit, once you have completed a mission the Lock stays lit even if you lose a ball, once you have completed all 3 missions and locked 3 balls the wizard mode automatically starts.
Now for the fun part, don't listen to the babble going on, just press A which will start the balls, you have a 30 second ballsaver and you do not want to waste it, in fact you will be abusing it. You need to use the 30 seconds for the tough shots, Storm & Cyclops and then any others are a bonus, but I'd try for Wolverine and maybe Colossus. You may well hit Iceman, Jean Grey and Nightcrawler by chance anyway.
The first ball drops to the middle of the table, ignore it, let it drop through as ball 2 drops shortly after just above the top left flipper giving you a free shot to Storm. The next ideal shot would be off the bottom right flipper up Wolverine orbit and onto the Cyclops orbit from the top right flipper. You can then use the rest of the 30 seconds keeping 3 balls and knocking out any lanes as a bonus.
Eventually you will lose a ball, once you have just 2 left, ideally you want to trap one on either flipper. In this position you have easy shots to Jean Grey off the right flipper, if you keep left flipper held this generally returns the ball to the right flipper anyway. Also shots to Colossus, Iceman and Nightcrawler are not to bad, the best method being hit the ball on the bottom right flipper up the unite ramp, giving you time on the left flipper to hit one of the 3 ramps I just mentioned.
Finally with all 7 lights out, one last shot up the unite ramp to defeat a sentinel.
Now at this stage I messed up, so did the 3 side missions again, locked the balls and continued to defeat sentinel number 2.
Sorry for the long description, but if you listen to any of this its to play smart whilst the ballsaver is on.
If you want more details on the other method or any tables in the series refer to Zen's site and look up shoryukentothechin, the descriptions of everything to do and activating extra balls, is laid out in detail with pictures. Essential viewing if you want to 100% this game. my respect to those who completed before me and anyone who follows.
You want to vote negative, go for it, I frankly couldn't care less, to anyone this helps, you are quite welcome.