Single leg and double leg takedown submission reversals are L2+R2 plus right stick down. The moves list says guillotine single leg reversal is L2+right stick down, but I can only get it to work L2+R2 right stick down.
Guillotine reversal from sprawl is L2+R2+ right stick down also. Kneebar reversal is L2+R2 plus right stick towards opponent, same direction you normally deny that transition.
Single and double leg takedown from clinch can be reversed.