Obelisk

A thirty-foot-tall obelisk ringed by seven smaller standing stones rises from the crest of this hill. A tall man wearing tattered robes strides between the standing stones, gesticulating wildly and screaming curses into the wind.

A pit fiend under the order of Zariel imprisoned the angel inside this circle of standing stones. To torment his adversary, The pit fiend revealed that the secret to escaping the prison was hidden in the arcane runes etched across the standing stones. Ever since, the tormented angel has tried futilely to solve the riddle and escape. The magic of the obelisk prevents the angel from leaving the circle and stops any form of divination magic from affecting the stones or targeting a creature inside their perimeter.
The angel claims that each standing stone is keyed to one of the eight schools of magic (abjuration, conjuration, divination, enchantment, evocation, illusion, necromancy, and transmutation), and he urges the characters to aid him in. Characters who examine the standing stones and succeed on a DC 15 Intelligence (Arcana) check discern that the arcane runes do indeed relate to the eight schools of magic.
The angel requests that each character places a hand upon a different stone. When their hands are in place, the angel begins to chant. The air fills with ozone as lightning courses over the standing stones. Each character who participates in the experiment takes 22 (5d8) lightning damage and suffers an additional effect based on the school of magic associated with the standing stone that the character touched, as noted in the Standing Stone Effects table. the angel's latest attempt to escape his prison has succeded.

School	Effect
Abjuration	You gain a +2 bonus to AC for the next 24 hours.
Conjuration	A monodrone appears in an unoccupied space within 5 feet of you and follows you around until it’s destroyed. It is indifferent toward all creatures, including you.
Divination	You gain the benefits of a true seeing spell for the next hour.
Enchantment	The standing stone casts confusion on you (save DC 15). The spell lasts for 1 minute.
Evocation	The standing stone casts magic missile, targeting you with five missiles.
Illusion	An illusory swarm of harmless bats or pigeons (DM’s choice) flutters over your head for the next hour. A dispel magic cast on the swarm ends the effect.
Necromancy	You also take 30 necrotic damage from the standing stone.
Transmutation	Your skin turns blue for the next 24 hours. A remove curse spell ends the effect on you.