This one was the last achievement I needed in order to complete the Marvel add-on and hit 850/850. It annoyed me because there are plenty of people who have unintentionally obtained this achievement during regular play. Here's the scoop on what I feel is the "easiest" way to get this. It's still pretty difficult.
1) You need to get to Doc Ock Stage 2. At the start of stage 2 he stays towards the top of the playfield for 10-15 sec and throws balls back at you if you hit them up the left ramp, or up the chute towards the bumpers. In fact, I don't think you can accomplish this during Doc Ock stage 1 because he doesn't throw the balls back at you.
2) I activate Doc Ock by shooting the left ramp, and letting the ball drain to the upper left flipper. I then make the "jump" shot through the roof. When the trapped ball is released, I shoot the Doc Ock hole. You need to do this *twice* in order to activate Doc Ock mode.
3) DON'T activate stage 2 unless you ALREADY have two shots up the goblin ramp. Once you have 2 shots up the goblin ramp (the third shot will start the goblin mode), then you are ready to activate Doc Ock stage 2.
4) My pattern goes like this: activate doc stage 2. the ball drains to the left flipper. get off a shot up the goblin ramp. this will activate goblin mode and you should still have about 5-7 seconds of the doc throwing balls at you.
5) Try to trap the silver ball on a flipper. Before I got it, people told me that once he grabbed a pumpkin ball I would have to try to loose the silver ball on purpose. That's BS. If you *wait* until he grabs a pumpkin ball it will be too late. He lets go of them too quickly for you to intentionally lose the silver ball. Instead you have to be ready to let the silver ball drain right as you shoot the pumpkin ball from the other flipper. If done right, the silver ball will drain just as the doc grabs a pumpkin.
Another thing I noticed. If you can get to goblin stage two, you'll have two pumpkins to work with when the mode is activated. Some people might think this is easier as there is more of a "random" chance of you hitting a pumpkin ball up towards Ock. I agree, but I also noticed it's hard to ensure a controlled trap of the silver ball.
Good luck. Once you've played this table enough it really shouldn't be too difficult to prep the table into the setup above. Once you get the hang of that, I estimate 30-45 min of trying should earn you this achievement.