This is pretty close to how I would do it. Here's my write-up for your consideration:
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Shroud
Concentration : Yes
Skills : Arcane, Primal and Verse
Basic Spell : Arcane, Primal, and Verse spellcasters possess the ability to hide objects and creatures, even making themselves invisible! The character selects one Silhouette 0 target they are engaged with, then makes an Arcana, Primal, or Verse check. The default difficulty of the check is Easy. If the check is successful, until the end of the character's next turn, increase the difficulty of any check made to see the selected object by one, and further increase the difficulty by one for every uncancelled [SUCCESS][SUCCESS] after the first. Additionally, increase the ability of any Stealth checks made by the target by one, and further increase the ability by one for every uncancelled [SUCCESS][SUCCESS]. The target of the base spell may not be the caster, even if the caster is Silhouette 0.
Additional effects:
+1D | Additional Target: The spell affects one additional target within range of the spell. In addition, after casting the spell, you may spend [ADVANTAGE][ADVANTAGE] to affect one additional target within the range of the spell (and may trigger this multiple times, spending [ADVANTAGE][ADVANTAGE] each time).
+1D | Range: Increase the range of the spell by one range band. This may be added multiple times, increasing the range by one range band each time.
+1D | Medium Shroud: The spell may target an object or creature up to Silhouette 2, and may include the caster.
+2D | Displacement: The spell refracts light surrounding the target, making the target appear not quite where it actually is. The target gains melee and ranged defense equal of 1, and further increases this source of melee and ranged defense by one for every uncancelled [SUCCESS][SUCCESS] after the first.
+2D | Empowered: The spell increases the difficulty of any check made to see the selected object by one per uncancelled [SUCCESS] rather than the normal effect. This effect does not modifiy the Displacement effect.
+2D | Grand Shroud: The spell may target an object or creature up to Silhouette 4.
+3D | True Invisibility: The spell grants true invisibility to the target. The target may not be detected visually in by any mundane means.
Edited by Simon Retold