Ancient Abyssal Armoured Giant

Legendary Resistance (3/Day). If the giant fails a saving throw, it can choose to succeed instead.

Shadow Bending. Cast Darkness as a bonus action

Weak Point. Hit the hole in its armour with radiant damage which will be doubled, that will cause it to make a blood curdling howling roar of agony. Also if it loses  over 5% of its health when the back of its nkess or attacked it will fall prone until it stands up on its turn.

Spellcasting. The giant is a spellcaster. Its spellcasting ability is Intelligence (spell save DC 16, +6 to hit with spell attacks). The giant has the following warlock spells:

Cantrips (at will): Blade ward, Eldritch blast, Sword Burst

1st level (3 slots): Arms of Hadar, Armour of agathys, Witch bolt, Hellish rebuke

2nd level (2 slots): Hold person, Misty step, Shatter

3rd level (2 slots): Fear, Counterspell, Hunger of Hadar

Multiattack. The giant makes three flail attacks or two bow attacks.

Flail. Melee Weapon Attack: +9 to hit, reach 13 ft., one targets, 3d12+8 bludgeoning damage.

Bow. Ranged Weapon Attack: +9 to hit, range 60/450 ft, one target. 3d10+8 piercing damage.

Dark Soul Surge (Recharge 5-6). Ranged Attack: +9 to hit, range 150 ft, one target. 2d18+8 necrotic damage.

Empowered Flail (1 Action). Melee Weapon Attack: +9 to hit, reach 15 ft., three targets, 3d12+8 bludgeoning damage plus 1d12 necrotic damage.

Empowered Bow (1 Action). Ranged Weapon Attack: +9 to hit, range 80/500 ft, three targets. 3d10+6 piercing damage plus 1d12 necrotic damage.

Mind Shadow (1 Action). One creature within 100ft must make a DC 16 intelligence saving throw and become blinded for 1 minute if you fail or 1 psychic damage if you pass.

Abyssal Roar (1 Action). All creatures in a 50ft long and 10ft wide cone must make a DC 18 constitution saving throw and on failing takes 1d6+2 thunder damage and becomes deafened for 1 minute and on passing you become deafened for 1 turn. 

Frightful Presence. Each creature of the giant's choice that is within 120 feet of the giant and aware of it must succeed on a DC 16 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 itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the giant's Frightful Presence for the next 24 hours.

Shield block. +6 AC for 1 turn.

Shield Bash. Melee Weapon Attack: +9 to hit, reach 10 ft., one target, 2d12+8 bludgeoning damage.

The giant can take 5 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 giant regains spent legendary actions at the start of its turn.

Detect. The giant makes a Wisdom (Perception) check.

Dark Magic. Cast a cantrip.

Greater Dark Magic (Costs 1 Action). Cast a 1st level spell without using a spell slot.

Dark Shell (Costs 2 Actions). The giant gains +6 AC and gains immunity to radiant damage for 1d4 turns and has a darkness spell cast, centered on it for the effects duration.

Dark Recovery (Costs 3 Actions). The giant uses the darkness within to repair its armour, regains 1d12+17 hit points.

Dark Recovery (Costs 4 Actions). The giant uses the darkness within to repair its armour, regains 1d12+17 hit points.

Dark Recovery (Costs 5 Actions). The giant uses the darkness within to repair its armour, regains 1d12+17 hit points.