Hi,
Currently expressions are not available in Combustion.
There is the parenting and targeting of layers available. You cannot link effects paramenters together but you can copy keyframes from one value to the next which would be performing the same function essentially.
In terms of working with the curve in the timeline, there is a facility called Math Operations which is from our systems products. This tool can simulate some of the functionality in expressions….
Regards
Grant
Discreet UK