To get the acheivement "BOY WONDER", try playing the board "Little Fun at the Big Top" and when you see the boats in toxin, do the 20 back flips as Robin. It is easy at this location because there is a big area to keep flipping, flip from one wall to the other. It is easiest to go from the right wall to the left.
It's more of a glitch then a hint, free coins glitch!!!!!!
Added 25 Aug 2011, ID #7693
On some levels, if you use mr. Freeze, when you see a guy with a ? Above him, use mr. Freezes freeze gun, keep holding the button and coins should keep on coming out of the guy with the ? Above him. I only fond out about this by accident. So happy free coinage day to you all.
In this achievement you must unlock every villain character. Simply play through the villain story line. You will unlock all characters through this method except for Hush. Find and save all 25 hostages to unlock Hush.
I was playing, with my friend, in the jocker's revenge part 1. I picked up the ice creame truck ( with jocker inside) and 1 was on the floor another was in the hand of the claw. Every time I lifted it the first jocker would act like he was dangling. I droped the icecreame truck and jocker2 fell out. When I lifted the truck joker2 outside the truck wwould lift up. I don't know if joker2 can be played with by a player three.
To defeat Mr.Freeze, Pision Ivy, & Two-Face you have to hit them in the back. If your batman then start fighting either of these villians and hit Y to switch to robin. Make sure robin is DIRECTLY BEHIND the villian and start hitting X.