Custom emails automatically generated based on participants filling in drupal forms
The list of tokens you see when editing a template changes depending on where you're editing from.  Unfortunately, CiviRules doesn't expose event/participant/contribution tokens in the drop-down - but if you use them in the email, they WILL work.

To see the tokens you may want to use, create a new Scheduled Reminder (**Administer menu » Communications » Scheduled Reminders), and create a new reminder based on an event.  You should be able to see event etc. tokens (see screenshot below).  Then either save as a new template, or simply copy the tokens into an existing one.