Elijah Namtar’s Absorb Extra Planar Being

The most powerful thing a conjuration wizard can do, when summoning a creature from outside the material plane, the wizard can take the creatures abilities and health pool. The creature may make a charisma save but if it is within a magic circle the creature has disadvantage.

While the wizard takes the power from the creature, the creatures soul lives inside the caster. Depending on the size of the creature, the caster must make a wisdom saving throw, 5 for a tiny, 10 for small so on and so forth. If the wizard fails, they must make a constitution save or expel the creature from their body. If they succeed, they take one level of exhaustion until they remake the save the next day.