Wookieepedia has its limits. Fairly often, when reading Star Wars books, I find significant details and precedents that don't make it onto Wook. I've tried editing them in, with moderate success, but Wook's editor culture is...not welcoming of outsiders. So rather than haggle with derps, I've decided to present some of my findings here, in character. Jorus is as good a mouthpiece as any; he spent years as Master of First Knowledge, handling Jedi and Sith holocrons; he's also been just about everywhere. So, without further ado: the Mask of the Wyrm ritual from the wordless comic 'Sithisis.'

***​

I've taken to calling this ritual the Mask of the Wyrm. It's vicious, disgusting alchemy, but I'll lay it out here for reasons that should become obvious. Just as obviously, don't show this to anyone who might actually use it.
This is one of the most complex and demanding rituals I've ever seen. Frankly, there are implications at every stage that I don't feel qualified to grasp. If Rave was still alive, I'd ask her. I found all this in her notes. The account is fragmentary and doesn't offer a lot of explanation. Rave wrote most of it down in her own private shorthand, and her handwriting was terrible. I had to call in the Underground's decryption people at a couple points.
First off: materials. There's a chest-sized, floating holocron of unusual design, almost hourglass-shaped, like two pyramids with their flat sides connected by a short wasp waist. The topmost corner opens like the capstone compartment of some other Sith holocrons. Inside, though, there isn't a crystal, but a wormlike critter, probably a Sith Wyrm variant. There's a huge, special crystal, about three times as tall as an adult human. Rave's notes suggest this is probably some kind of alchemical chrysalis for nurturing a similar worm.
Step one: Blood sacrifice. Open the huge floating holocron, cut palm, drip blood inside.
Step two: First battle. The worm will consume the blood and attack you. Eat it alive.
Step three: The worm chews your guts, a more profound sacrifice than the drop of blood. As it dies, you experience transcendence, a broadening of consciousness. You sense the regard of many Sith Lords who have come before you. You have the power to work the Force on a diffuse but grand scale.
Step four: Spend that power doing something that will cause fear to Force-sensitives. The given example is a thunderstorm that covers a good chunk of a planet, overlapping the Jedi Temple.
Step five: The massive crystal collects their fear and reflects their images in its facets. At this point, Rave believed that the second worm, the one inside the crystal, was empowered and alchemized by the crystal, with the fear as fuel - a Consume Essence variant crossed with highest-level alchemy.
Step six: The crystal shatters. The worm, now the size of a dewback or larger, attempts to kill you.
Step seven: Allow the worm to eat you.
Step eight: Destroy the worm from within using Force Lightning.
Step nine: Emerge from the worm with the ravages of the Dark Side hidden from your face and body. Effectively, the Sith spell known as Mask. This may even be the primary ritual behind that spell; Rave never knew Mask, so she couldn't say for sure.
There's also a note here regarding the use of Force Dispersers to keep the ritual hidden. Clearly, it needs to take place on a planet where there are Jedi; just as clearly, the practitioner needs to hide from us for this time- and power-intensive ritual to succeed.
What's important here is that we question thunderstorms and other large-scale disasters on worlds with Jedi temples. We need to carefully examine any mention of Sith worms. And we need to remember that a Sith Lord may be able to conceal his personality, Force-sensitivity, and politics from his closest friends.