Barbed Giant

Armored Shell. If the Barbed Giants AC is 10 or more, it has resistance to all nonmagical piercing, bludgeoning and slashing damage from all attacks. If it's AC is 12 or more, It gains use of the Barbed Form ability. If it's AC is 14 or more, it gains use of the Enlarged Form ability. If it's AC is 16 or more, it's barbed form ability deals an extra 1d10 damage. If it's AC is 18 or more, it gains magical resistance. It's max AC is 20. It's AC resets to 2 after one hour.

Spikey Outrage. When the Barbed Giant is mortal, their spikes lash out at the world around them. Any creature in 10ft. of the Barbed Giant must succeed on a DC 17 Dexterity saving throw. If it fails, it takes 36 (6d12) piercing damage, is pushed 15 feet away from the Barbed Giant and is knocked prone. If it succeeds, it takes half the amount of damage and isn't knocked back or knocked prone.

Barbed Form. Any creature that starts it's turn within 5ft. of the Barbed Giant takes 5 (1d10) piercing damage.

Magical Resistance. The Barbed Giant has advantage on saving throws against spells and other magical effects, and if the Barbed Giant is subjected to an effect that allows it to make a dexterity saving throw to take only half damage, it instead takes no damage if it succeed on the saving throw, and only half damage if it fails.

Enlarged Form. The Barbed Giant is counted as creature size Huge. 

Multiattack. The Giant makes two fist attacks, one with it's left hand and one with it's right

Fist. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 11 (1d10 + 6) bludgeoning damage. (For every attack that hits per hand, the damage increases by 1d10 piercing damage each time, for a maximum of 6d10. Exp. It's the third attack with the right hand, so the damage would be 3d10 + 6 piercing damage. This resets after one hour.)

Rebar. Ranged Weapon Attack: +5 to hit, range 60/240 ft., one target. Hit: 26 (4d12 + 2) piercing damage. On a hit, the creature must make a DC 17 Dexterity saving throw. On a success, the creature takes regular damage. On a fail, the creature is knocked prone and it's speed becomes zero because the Rebar impaled it on the ground.

Crushed Boulder (Recharge 5-6). The giant crushes a boulder in it's hands and hurls a shower of splintered stone in a 60-foot cone. Each creature in that area must make a DC 17 Dexterity saving throw, taking 35 (10d6) piercing damage on a failed save, or half as much damage on a successful one.

Armor Up. When the Giant is hit by an attack, it can use it's reaction to roll 1d8+2. That amount is then added to it's AC.