Dungeon Oddities: Necrotic Altars

Below is our 5th in a series of weird things to find in a dungeon/cavern/ruins. Each is an unusual event or item which bestows strange effects on any encounter there.

Necrotic Altars

divine, magic, necromancy

The altar before the group has an odd, dark shimmer to it, almost as if it possesses life or at least magical properties. Possible effects: (Roll a d6 or choose):

1. The spirit of the last creature sacrificed on the altar is still here. If evil (or corrupted during the ceremony) it adds necrotic damage to the attacks of evil creatures.  If it was good and not ceremonially corrupted, it fights the evil influence and instead adds radiant damage to the attacks of good creatures.
2. Divine spells by a caster of a religion opposite (or nearly) the altar’s religion may be interrupted/ruined by the altar’s power if cast within 40′.  A caster must make a concentration or similar check or else the spell fails, but the spell slot is not lost.
3. The altar is able to pull the life-force (hit points) of a creature opposed to the altar’s religion and bestow the same life force to a follower of the altar’s religion. The target makes a saving throw to prevent this.
4. Followers of the altar’s religion gain one action per turn when they are within 40′ of the altar.
5. If the altar senses foes (anyone with an alignment or religion opposed to its own) within 20′ of it, the altar is able to summon protectors such as elementals, demons, etc.
6. Given the right ceremony and circumstances, the altar is capable of greatly augmenting the divine magic of a priest who follows the same religion.  Perhaps it can form a portal to another realm, summon a powerful entity, banish individuals to another plane, cause (or prevent) a major disaster, or something else on that scale.