Aberrations are utterly alien beings. Many of them have innate magical abilities drawn from the creature’s alien mind rather than the mystical forces of the world. The quintessential aberrations are aboleths, beholders, mind flayers, and slaadi.
Here is a list of all of the special traits for monsters with the Aberrations type in the Dungeons & Dragons 5e Monster Manual:
Aberrant Ground. The ground in a [distance] radius around the [listed creature] is doughlike difficult terrain. Each creature that starts its turn in that area must succeed on a DC [X] Strength saving throw or have its speed reduced to [X] until the start of its next turn.
Monsters: gibbering mouther
Advanced Telepathy. The [listed creature] can perceive the content of any telepathic communication used within 60 feet of it, and it can’t be surprised by creatures with any form telepathy.
Monsters: flumph
Amphibious. The [listed creature] can breathe air and water.
Monsters: aboleth, chuul
Antimagic Cone. The [listed creature]’s [body part] creates an area of antimagic, as in the antimagic field spell, in a [distance] cone. At the start of each of its turns, the [listed creature] decides which way the cone faces and whether the cone is active. The area works against the [listed creature]’s own eye rays.
Monsters: beholder
Damage Transfer. While attached to a creature, the [listed creature] takes only half the damage dealt to it (rounded down), and that creature takes the other half.
Monsters: cloaker
Detect Sentience. The [listed creature] can sense the presence and location of any creature within [distance] of it that has an Intelligence of 3 or higher, regardless of interposing barriers, unless the creature is protected by a mind blank spell.
Monsters: intellect devourer
False Appearance. While the [listed creature] remains motionless without its underside exposed, it is indistinguishable from a [item the creature mimics].
Monsters: cloaker
Gibbering. The [listed creature] babbles incoherently while it can see any creature and isn’t incapacitated. Each creature that starts its turn within [distance] of the [listed creature] can can hear the gibbering must suscceed on a DC [X] Wisdom saving throw. On a failure, the creature can’t take reactions until the start of its next turn and rolls a d8 to determine what it does during its turn. On a 1 to 4, the creature does nothing. On a 5 or 6, the creature takes no action or bonus action and uses all its movement to move in a randomly determined direction. On a 7 or 8, the creature makes a melee attack against a randomly determined creature within its reach or does nothing if it can’t make such an attack.
Monsters: gibbering mouther
Innate Spellcasting. The [listed creature]’s innate spellcasting ability is [ability and spell save DC]. It can innately cast the following spell requiring no components: [spells]
Monsters: death slaad, gray slaad, green slaad
Innate Spellcasting (Psionics). The [listed creature]’s innate spellcasting ability is [ability and spell save DC]. It can innately cast the following spell requiring no components: [spells]
Monsters: mind flayer
Keen Sight. The [listed creature] has advantage on Wisdom (Perception) checks that rely on sight.
Monsters: nothic
Light Sensitivity. While in bright light, the [listed creature] has disadvantage on attack rolls and Wisdom (Perception) checks that rely on sight.
Monsters: cloaker
Limited Telepathy. The [listed creature] can magically transmit simple messages and images to any creature within [distance] of it that can understand a langauge. This form of telepathy doesn’t allow the receiving creature to telepathically respond.
Monsters: otyugh
Magic Resistance. The [listed creature] has advantage on saving throws against spells and other magical effects.
Monsters: blue slaad, gray slaad, green slaad, death slaad, mind flayer, red slaad, slaad tadpole
Magic Weapons. The [listed creature]’s weapon attacks are magical.
Monsters: death slaad, gray slaad
Mucous Cloud. While underwater, the [listed creature] is surrounded by transformative mucus. A creature that touches the [listed creature] or that hits it with a melee attack while within [distance] of it must make a DC [X] Constitution saving throw. On a failure, the creature is diseased for [time]. The diseased creature can breathe only underwater.
Monsters: aboleth
Negative Energy Cone. The [listed creature]’s [body part] emits an invisible, magical [distance] cone of negative energy. At the start of each of its turns, the [listed creature] decides which way the cone faces and whether the cone is active. Any creature in that area can’t regain hit points. Any humanoid that dies there becomes a [undead type] under the [listed creature]’s command. The dead humanoid retains its place in the initiative order and animates at the start of its next turn, provided its body hasn’t been completely destroyed.
Monsters: death tyrant
Probing Telepathy. If a creature communicates telepathically with the [listed creature], the [listed creature] learns the creature’s greatest desires if the [listed creature] can see the creature.
Monsters: aboleth
Prone Deficiency. If the [listed creature] is knocked prone, roll a die. On an odd result, the [listed creature] lands upside-down and is incapacitated. At the end of each of its turns, the [listed creature] can make a DC [X] saving throw, righting itself and ending the incapacitated condition if it succeeds.
Monsters: flumph
Regeneration. The [listed creature] regains [X] hit points at the start of its turn if has at least 1 hit point.
Monsters: death slaad, gray slaad, green slaad, red slaad
Sense Magic. The [listed creature] senses magic within [distance] of it at will. This trait otherwise works like the detect magic spell but isn’t itself magical.
Monsters: chuul
Shapechanger. The [listed creature] can use its action to polymorph into a Small or Medium humanoid, or back into its true form. Its statistics, other than its size, are the same in each form. Any equipment it is wearing or carrying isn’t rtansformed. It revers to its true form if it dies.
Monsters: death slaad, gray slaad, green slaad
Spellcasting. The [listed creature] is a [X]-level spellcaster. Its spellcasting ability is [ability and spell save DC, to hit with spell attacks]. The [listed creature] has the following [caster type] spells prepared: [spells]
Monsters: mind flayer arcanist
Telepathic Shroud. The [listed creature] is immune to any effect that would sense its emotions or read its thoughts, as well as all divination spells.
Monsters: flumph