In Lego Batman 2, the NDS, 3DS, and PS Vita versions all have stud multipliers. These are crucial for getting 100%, as it makes collecting studs way faster. However, the Mobile version does not have these multipliers (as it encourages in app purchases). To counter this, you can replay a Bonus Mission multiple times to get all the studs needed at a fairly fast pace (around 20 minutes). This saves an INSANE amount of time for, say, the 100% Mobile run.

Here's a video that shows this trick more in depth: VIDEO

Note: It takes 6 rounds to get all the studs necessary, definitely not 15 rounds as the video says.

I am unsure if this trick saves time on the other versions of this game.