I am a Reason user since version 1. One of the things that was so innovative about Reason at the time was Dr:REX which could run stereo rex-loops. This supa dupa device has transformed into Dr OctoRex since Reason 5 with an additional feature-set and 8 slots for loops. But even with Dr:REX, using only one loop, you could do cool things when automating its parameters. Check my example I made many years ago using my own loop and playing with the parameters:

Flow ~ undull repetitions