The Immediate Nimbus is a powerful aura directly surrounding the mage, wrapping close to her soul and flashing out as the Supernal World ebbs and flows against her.
When she casts a spell, her Immediate Nimbus becomes visible to those with any active Mage Sight, regardless of the Arcana she’s using to cast. The Immediate Nimbus appears based mostly on the character’s Path. It’s a force, a halo of raw creation stuff. Sometimes, this is visible — sometimes it’s a sensation, a smell, or a muddy, primal emotion.
Here are a handful of examples:
For Thyrsus, this might look like a mist of blood, or might cause a deep rutting instinct.
Moros might cause subtle rot around them, or melancholy.
Obrimos bask in holy light, or cause remarkable inspiration.
Acanthus appear as if time bends around them, or cause fatalism.
Mastigos glow with a sickly green fire, or cause temptation to swell in onlookers.
When the Immediate Nimbus flares, it causes a Nimbus Tilt unique to your character, with a strength depending on what caused the flare. If the Nimbus flared because of a spell, use the spell’s Potency as the Nimbus’ strength, and the Tilt lasts for the spell’s Reach in turns or one turn at a minimum.
Alternatively, once per scene a mage can force her immediate Nimbus to flare for a single turn without casting a spell by spending a Mana.
In this case, roll the character’s Gnosis and use successes as the Nimbus’ strength. Deliberate flares like this are visible even in the Fallen World and can therefore affect characters not using Mage Sight, although Sleepers will suffer Quiescence after the Tilt ends.
Compare the Nimbus strength to any witness’s Resolve. If a character’s Resolve is equal to or lower than the Nimbus strength, the Tilt takes effect. If for whatever reason a character is aware of the effects, she can willingly submit to the Tilt regardless of her Resolve.
Mages can pit their own Nimbus against the aura as per the Interactions with Other Auras rules. While characters without Mage Sight cannot see the aura, the subtle cues still affect them with the Tilt. This is almost always imperceptible, but some particularly clued-in witnesses may note when something’s awry.