Spell: Vampiric Lanthorn

Vampiric Lanthorn​

Necromancy (shadow)
Level: Sorcerer 4, Wizard 4
BoXM: Wizard 7
Casting Time: 1 standard action
Components: V, S, F (an inscribed and carefully prepared silver lantern fueled with pure oil
   and shadowstuff; such a lantern always has hardness 4 and 30 hp, and it costs 400 gp)
Effect: One 30-ft.-radius circle
Duration: 1 round/level or until lantern destroyed
Saving Throw: Fortitude negates
Spell Resistance: No
Source: The Mage's Tower website

By lighting a ritually prepared lantern, you generate an area within which the life is drawn out of all creatures around you and channeled through the lantern into you. At the time of the spell’s casting, all creatures within the lantern’s light must make a Fortitude save each round that they remain in the area. Success means they are unaffected that round. Failure means they suffer 2d4 hit point loss, and you gain hit points equal to 1d4 per creature damaged in this way. You retain these points for 10 rounds after the spell ends.

If the lantern is destroyed, the spell ends immediately, and you lose all leeched hit points.
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GM Note

The BoXM entry is for players playing in the Arcane Age of Greyhawk campaign. It is based on Monte Cook's Book of Experimental Magic. I cannot recommend it enough.