This is the last of the spell books from Dragon Magazine #92, by Ed Greenwood. I only converted over 1 of the 4 spells that were listed with it, Grimwald's Greymantle, and I had to trim that down quite a bit. Of the other spells, one was just a more powerful burning hands, which can be duplicated by using a higher level slot in 5e. The other 2 had too many fiddly bits to make into usable spells.
The Tome of the Covenant
This book is large, square, and (judging from Elminster’s description) approximately two feet on a side. It is fashioned of cured white elkhide stretched over finger-thick boards of black wood, and both outside covers bear a rune in the center, depicting four arrows meeting in a circle, thus:
Four white vellum pages are sewn to the hide spine within.
History and Description
The Tome is the creation of the four most powerful (of their time) mages of the North, who formed the Covenant, an alliance (basically neutral good) founded to enforce a peace between warring tribal kingdoms, and to build the collective power and prosperity of the Northlands against the coming confrontation with the orcs and their kin.
The Covenant has long been inactive: Grimwald and Presper disappeared on a journey of exploration into other worlds than this; Agannazar is believed to have perished in the destruction of the School of Wizardry at Neverwinter by the Red Wizards of Thay; and Illykur is known to have sacrificed himself in the Green Tower of Thulnath to destroy the arch-lich Ruelve.
The Tome was made to commemorate the founding of the Covenant, and as a source of power and a worship symbol for the apprentices who were intended to follow in the Four Founders’ footsteps and become new members of the pact (none did). Each of the Four Founders contributed one unique spell to the work, and each of these spells appears alone on its own page. The spells appear with no names; they have acquired colloquial names through description of the book by various writers in the North, and by use of the spells by the original apprentices of the Four (and subsequently, in turn, by their apprentices).
These apprentices, now themselves powerful workers of magic, are not identified by Elminster. The sage does say that they did not cooperate as their masters had, but split in dissension, one of them presumably bearing the Tome. Its present owner and whereabouts are uncertain.
5th level necromancy
Casting Time: 1 action
Components: V, S, M (a bone or small animal skeleton)
Duration: 1 round/level
When you casts this spell, a silvery-grey radiance is produced and if the target fails Constitution saving throw, expands to envelop them in an aura, or mantle. While this shimmering radiance is in effect, curative spells, healing, and regeneration of natural or magical nature will not be effective within the confines of the mantle; thus, a troll could not regenerate, a ring of regeneration would not operate, a potion of healing would have no effect, and so forth.