Aw man level 13 is hard... the way I did it was get some of the little ones then get the bigger one in the bottom left corner and then fight like hell to get the big one. Once you maintain the big one you can capture any of the red ones with low numbers.
For me the best way to get the impossible badge was to make sure that I made the tower stay as low as possible. If it wasn't, that the thing would start to shake like Michael J. Fox.
 "Nano War"){kind=icon}
 "Balance Balls 2"){kind=icon}
 "99 Bricks"){kind=icon}
 "SHIFT 3"){kind=icon}
 "6 Differences"){kind=icon}