A Puppet, now mine: The Abyssal Horror can cast any spells of the Wizard that summoned it at will. Its spell save DC is the same as the Wizards and Its health also multiplies by the Wizards level.

Life to consume: The Abyssal Horror can sense the position of any living creature up to 75ft away.

Formless: The Abyssal Horror may not use the Dash action but ignores the negative effects of difficult terrain and can move up walls freely.

Darkness unleashed: The Abyssal horror can use the boon of the Artifact that the Wizard who summoned it possesses, without paying a price.

Necrotica Sano Choose a corpse of a creature with at least size category medium 1up to 10ft away from you. The corpse is destroyed as you consume it and regain 2d10+3hp.

Skewer Melee Weapon Attack: +10 to hit, reach 10 ft., 1 target. Hit:  2d8+3 necrotic damage and 2d8+3 piercing damage. 

Gazing Beams Ranged Weapon Attack: +8 to hit, range 100 ft., 3 targets. Hit:  4d4+3 force damage. Any creature Targeted by an Augury Beam has to make a DC 15 Dexterity saving throw or take 2d8+8 Force Damage as the beam causes an explosion when it touches the ground. If the saving throw is successful it takes half the damage.

Gore When a creature you can see up to 20ft away from you moves, you may attack it with Skewer and increase its range to 20ft for that attack.

The Abyssal horror may take a Legendary action every time it takes damage. It can perform up to 3 Legendary action every turn and regains the spent uses upon starting its turn.

Aquired Scent (Costs 1 Actions) Choose a creature up to 10ft away from you. Your attacks gain advantage against it and heal for half the damage you deal to it. This effect lasts until the creature that you chose moves at least 15ft away from you.

Arcane Rupture (Costs 1 Actions) Cast a spell. 

Unstable Arcane Rupture (Costs 3 Actions) Cast 1d4-1 Spells centered at random creatures in range.