Sidechain compression is not the only effect you can create in Reason using the MClass compressor. Those smart people at propellerheads were insigtful enough to give the MClass compressor a Gain Reduction CV out. Which you can use to control any parameter you like.
Here I am using the compressor to pump an RV7000 Reverb Start by creating a Combinator to host the RV7000 this allows you control parameters that would not otherwise be controllable using CV’s. I’ve put the compressor in the combinator too just to keep things tidy. The Gain Reduction CV output is connected to the Rotarty 1 input on the Combinator. This allows Rotary 1 to be routed to the Dry/Wet parameter of the RV7000.
The overall effect of this setup isn’t that great, but the point is that you can use sidechaining to control any parameter in Reason.