How to use the Webform Serial in a Webform Rule? Is there a way to use the Webform Serial (not the SID) be used in a webform rule? 

I've tried the following with no success:

[data:serial]
[webform:serial]
[node:serial]


I do have Webform Rules &amp; Webform Tokens installed.
Have a look at comment #2 in issue #2572067, which states this:

The correct token for that is [submission:serial], but some module is going to have to make that token available to the rules module. Webform itself doesn't do that. I haven't tried it, but the Webform Rules modules would be the place to start.
The serial number is a relatively new feature, but I would have though it would work without an update to the Webform Rules module. If not, you might file an issue in that module's queue.