Cheapest priced copy (Scars of Mirrodin): $0.35 at Card Kingdom, near mint, their price list as of .
Flesh Allergy 
Sorcery · Uncommon · Scars of Mirrodin · #62
As an additional cost to cast this spell, sacrifice a creature.
Destroy target creature. Its controller loses life equal to the number of creatures that died this turn.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Scars of Mirrodin | 62 | Uncommon | $0.35 | $0.49 |
6 rulings from Wizards of the Coast
- 1 January 2011If the targeted creature is an illegal target by the time Flesh Allergy resolves, the spell doesn't resolve. No player will lose life.
- 1 January 2011You can target a creature you control, then sacrifice that creature to pay the additional cost. However, if you do, Flesh Allergy won't resolve for having an illegal target. You won't lose any life.
- 1 January 2011Flesh Allergy counts each creature put into a graveyard from the battlefield that turn, including token creatures, the creature sacrificed to cast the spell, and the targeted creature (if it is destroyed).
- 15 April 2013You must sacrifice exactly one creature to cast this spell; you cannot cast it without sacrificing a creature, and you cannot sacrifice additional creatures.
- 15 April 2013Players can only respond once this spell has been cast and all its costs have been paid. No one can try to destroy the creature you sacrificed to prevent you from casting this spell.
- 1 July 2013If Flesh Allergy resolves but the targeted creature is not destroyed (because it has indestructible or enchanted by an Aura with umbra armor, for example), its controller will still lose life.