You can connect a footswitch or expression pedal to the CTL 1 and 2/EXP jacks on the RV-200. Assign functions to the connected footswitch or expression pedal according to your use. For details on the connection method and function assignment, see "Overall settings (Menu)" and "Assigning functions to an external pedal" in the RV-200 Owner's Manual.
Using the jack as CTL 1/2: You can connect a footswitch (FS-5U, FS-6, FS-7; sold separately) and use it for fading in/out or switching memories.
Using the jack as EXP: You can connect an expression pedal (EV-30, Roland EV-5, etc.; sold separately) and use it to control the reverb time, reverb volume and so on.