The only whole grain mustard I could find at the store had garlic which worked out but you can use plain whole grain mustard if you want.
The original recipe calls for 3 habaneros and 6 Thai chilies to each jar which would have been wayyy too much spice.
I added the seeds, peppercorn to each jar since I was making multiple jars at once. The video has you adding it all to a pot and cooking it.
I have added all my notes on canning practices in a separate blog post here, make sure to read my notes before dealing with canning jars that will be held at room temperature.