This spell is a part of the Deconstruction spell chain and can be found in the Deconstruction rune stone.
The Worm is patient. This is perhaps the most important thing to understand about it. It does not rush. It does not strike. It finds a way in and then it waits, working slowly through whatever it has found purchase in, moving from the outside inward, from the obvious toward the subtle. It began with armor. Then flesh. Then the body's reserves of strength and endurance. And now, with the seniumancer deep enough into their craft to ask this of it, The Worm reaches further still. It reaches past the body entirely, into the mind. What it finds there is softer than bone and more vulnerable than flesh. The connections that allow a caster to reach their runic soul, to hold a spell together long enough to cast it, to sustain the focused will that magic requires; these are not physical things. They cannot be hardened or armored against. They simply exist, delicate and vital, and The Worm, once given permission, finds them extraordinarily easy to feed upon.
When the seniumancer casts Mental Decay they direct The Worm's hunger downward into a chosen area of the battlefield. A creeping wrongness settles over the space. It is not visible and not dramatic. It is felt only as a growing difficulty in thinking clearly, in reaching for the runic soul and finding it responsive. Every target within the area finds their Soul halved, their runic speed decreased by 1d4, and their runic power halved as The Worm quietly feeds on the mental and spiritual reserves that make magic possible. The seniumancer alone is spared, standing at the edge of what they have invited in. The effect does not end cleanly when the spell does or when a target moves beyond its reach. The Worm has already made inroads, and it does not simply stop because the invitation has been withdrawn. The diminishment lingers for 2 additional rounds, the mental decay continuing to work even after the source has gone. It is a reminder that some things, once started, finish in their own time.
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