Mindslicer Crystal (5e Hazard)
From D&D Wiki
A single mindslicer crystal fits in a 5-foot square space, and crystals are often found in groups. A creature that starts its turn or moves within 10 feet of a mindslicer crystal for the first time on its turn must succeed on a DC 15 Wisdom saving throw against the crystal's magic or take 10 (3d6) psychic damage and have disadvantage on Intelligence-based attack rolls, Intelligence checks, and Intelligence saving throws for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
A creature within 10 feet of a mindslicer crystal cannot be contacted by telepathy, and any creature that attempts to telepathically communicate with the creature must succeed on a DC 15 Wisdom saving throw or be affected by the crystal's magic. Creatures immune to psychic damage can telepathically communicate normally with the creature, while creatures resistant to psychic damage have advantage on the saving throw.
A mindslicer crystal has AC 17, 50 hit points and immunity to poison and psychic damage.