Barbaric Anomaly

Amphibious. The Barbaric Anomaly can breathe both air and water.

Wild Magic Surge. The Barbaric Anomaly has a 50% chance of experiencing a wild magic surge whenever it takes damage from something other than a wild magic surge.

Siege Monster. The Barbaric Anomaly deals double damage to objects and structures.

Innate Spellcasting (1/Day). The Barbaric Anomaly can cast prismatic spray without requiring concentration, DC 15.

Magic Resistance. The Barbaric Anomaly has advantage on saving throws against spells (specifically does not have advantage against other magical effects, including its own Wild Magic Surges).

Multiattack. The Barbaric Anomaly makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +18 to hit, reach 15 ft., one target. Hit: 38 (4d10 + 10) piercing damage. If the target is a creature, it must succeed on a DC 18 Constitution saving throw or suffer a random effect from the Wild Magic Surge table.

Claw. Melee Weapon Attack: +18 to hit, reach 10 ft., one target. Hit: 28 (3d10 + 10) slashing damage.

Tail Swipe. Melee Weapon Attack: +18 to hit, reach 20 ft., all creatures in the area. Hit: 30 (3d10 + 10) bludgeoning damage, and each affected creature must succeed on a DC 18 Strength saving throw or be knocked prone.

Claw. Melee Weapon Attack: +18 to hit, reach 10 ft., one target. Hit: 28 (3d10 + 10) slashing damage.

The Barbaric Anomaly can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The Barbaric Anomaly regains spent legendary actions at the start of its turn.

Wild Magic Surge (Costs 2 Actions). The Barbaric Anomaly triggers a wild magic surge. Roll a d100 on the Wild Magic Surge Table to determine the effect.

Chaotic Strike. The Barbaric Anomaly makes one claw attack.

Ephemeral Shift. The Barbaric Anomaly magically phases through the Ethereal Plane for a moment, reappearing in a different location within 60 feet.

Primal Roar (Costs 2 Actions). The Barbaric Anomaly unleashes a primal roar, forcing all creatures within 30 feet to make a DC 18 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the Barbaric Anomaly's Primal Roar for the next 24 hours.

Not sure where to put wild magic table, but so here it is.

1. The Barbaric Anomaly and all creatures within 30 feet gain resistance to all damage for until the end of their next turn.
2. A burst of harmless confetti erupts in a 20-foot radius around the Barbaric Anomaly.
3. The Barbaric Anomaly is surrounded by spectral duplicates for 1 minute, as if under the effects of the Mirror Image spell.
4. A bolt of lightning strikes the Barbaric Anomaly, dealing 20 (4d8) lightning damage to it and all creatures within 10 feet.
5. The Barbaric Anomaly gains a fly speed of 60 feet for 1 minute.
6. A random creature within 60 feet becomes invisible for 1 minute.
7. The Barbaric Anomaly gains 30 temporary hit points.
8. The Barbaric Anomaly is affected by the confusion spell for 1 minute (no concentration required). DC 15 Wis save at the end of its turn to end the effect.
9. A rain of colorful sparks showers down in a 20-foot radius around the Barbaric Anomaly, causing creatures to become dazzled for 1 minute.
10. The Barbaric Anomaly casts color spray targeting a random creature within 60 feet.
11. All creatures within 30 feet of the Barbaric Anomaly are affected by the haste spell for 1 minute.
12. The Barbaric Anomaly's size increases by one category for 1 minute.
13. A brilliant light emanates from the Barbaric Anomaly, blinding all creatures within 30 feet for until the end of their next turn.
14. The Barbaric Anomaly gains a telepathic link with a random creature within 60 feet for 1 minute.
15. A stream of butterflies surrounds the Barbaric Anomaly, granting advantage on Charisma-based skill checks for 1 minute.
16. The Barbaric Anomaly becomes incorporeal for 1 minute, allowing it to move through objects and creatures.
17. All non-magical plants within 30 feet of the Barbaric Anomaly grow and blossom instantly.
18. The Barbaric Anomaly emits a calming aura, causing creatures within 30 feet to gain advantage on Wisdom saving throws for 1 minute.
19. The Barbaric Anomaly and all creatures within 30 feet gain vulnerability to all damage until the end of their next turn.
20. A zone of silence surrounds the Barbaric Anomaly, extending 5 feet in all directions, until the end of the Barbaric Anomaly's next turn.
21. The Barbaric Anomaly and all creatures within 30 feet are affected by the slow spell for 1 minute. DC 15 Wisdom Saving throw to escape its effects.
22. The Barbaric Anomaly's limbs elongate, increasing its reach by 5 feet for 1 minute.
23. A burst of noxious gas fills the air within 20 feet of the Barbaric Anomaly, causing creatures to become poisoned for 1 round.
24. A flaming horse appears (not a nightmare, but a horse on fire).
25. Grease is cast centered on the Barbaric Anomaly. DC 13 saving throw or fall prone.
26. A mature oak sprouts in an unoccupied space within 60ft of the Barbaric Anomaly.
27. The Barbaric Anomaly becomes a potted plant until the start of its next turn.
28. A Geyser lifts Barbaric Anomaly 50ft in the air until end of its next turn
29. A confused bear appears within 60ft for 1 minute
30. Grass instantly sprouts to 3’ tall within 20’, 1 minute
31. The Barbaric Anomaly and all creatures within 30 feet gain advantage on saving throws against spells for 1 minute.
32. The Barbaric Anomaly is Paralyzed until the start of its next turn
33. If the Barbaric Anomaly dies within the next minute, its ghost haunts its killer unless removed with the Wish spell 
34. A random creature within 60 feet is polymorphed into a harmless creature for 1 minute.
35. Everyone within 30ft of the Barbaric Anomaly is invisible for 1 minute or until they attack or cast a spell
36. A vortex of wind surrounds the Barbaric Anomaly, extinguishing all flames within 20 feet and dispersing fog for 1 minute.
37. The Barbaric Anomaly gains advantage on attack rolls until the end of its next turn.
38. Everything within 20ft of the Barbaric Anomaly is pulled 10ft closer to it. DC 17 Str save to resist.
39. The Barbaric Anomaly's voice becomes magically amplified, audible up to 300 feet away for 1 minute.
40. A sphere of silence envelops the Barbaric Anomaly, rendering it immune to sonic-based effects for 1 minute.
41. The Barbaric Anomaly and all creatures within 30 feet gain vulnerability to a random damage type until the end of their next turn.
42. A burst of radiant energy emanates from the Barbaric Anomaly, healing all creatures within 30 feet for 2d6 hit points.
43. The Barbaric Anomaly gains tremorsense with a range of 60 feet for 1 minute.
44. A spectral shield forms around the Barbaric Anomaly, granting it a +2 bonus to AC for 1 minute, unless this effect is already applied.
45. The Barbaric Anomaly's skin becomes purple, and smells like lavender for the next day.
46. A floating eye appears pointing towards the Barbaric Anomaly that has the effects of a Beholders main eye. 
47. The Barbaric Anomaly and all creatures within 30 feet gain the effect from a random potion of giants strength.
48. The Barbaric Anomaly gains a psychic scream ability, forcing all creatures within 30 feet to make a DC 18 Wisdom saving throw or become frightened for 1 minute.
49. The Barbaric Anomaly's limbs become ethereal, allowing it to pass through objects and creatures for 1 minute.
50. A spectral dragon appears near the Barbaric Anomaly, healing it 2d10