Magetainted

[Jades]

Sometimes, areas of high magical concentration become the location of major battles or destruction. On rare occassion, part of the karmic balance of these locations are twisted to the point where the creatures that inhabit them become perverted by the arcane force moving through the region.

Type Changes to Magical Beast
Abilities +2 STR, +4 CON
AC +2 to Natural Armor
special Attacks Aethyraegis 3/day. All enemies that do not have the magetaint template applied to them take 1d8 per HD of the base creature in damage.
SR equals 10+1/2 HD of the base creature

How does this look, and how should it affect the CR? +2?

(This could also happen in alchemical labs if potions spilt to the floor and mixed and were left there for weeks and rats ran through it or stuff like that.)

[Gralamin]

Sometimes, areas of high magical concentration become the location of major battles or destruction. On rare occassion, part of the karmic balance of these locations are twisted to the point where the creatures that inhabit them become perverted by the arcane force moving through the region.

Type Changes to Magical Beast
Abilities +2 STR, +4 CON
AC +2 to Natural Armor
special Attacks Aethyraegis 3/day. All enemies that do not have the magetaint template applied to them take 1d8 per HD of the base creature in damage.
SR equals 10+1/2 HD of the base creature

How does this look, and how should it affect the CR? +2?

(This could also happen in alchemical labs if potions spilt to the floor and mixed and were left there for weeks and rats ran through it or stuff like that.)
Defiantly a CR+2, at least.
Notice though you didn't mention exactly what could become it, so technically you can have undead running around like this (just make sure you say only animals and vermin may gain this template (or some such))

[MandibleBones]

What's the range on Aethyraegis?

[Jades]

Just adjacent, bah forgot to type that in... All adjacent foes.