Ancient labyrinth guard.

Stone to steel: the guardian hardens his form from stone to steel at 50% hp. adding 1D4 damage   AC increases to 18

Magic Resistance. The golem has Advantage on saving throws against spells and other magical effects.

Multiattack. The golem makes two attacks, using stone Blade, shield bash or force laser in any combination.

Stone sword. Melee Attack Roll: +5, {"diceNotation":"1d20+15","rollType":"to hit","rollAction":"stone sword"}, reach 5 ft. Hit: x (2d3 + 3) Bludgeoning damage plus  (2d6) Force damage.

Shield Bash. Melee Attack Roll: +5, {"diceNotation":"1d20+15","rollType":"to hit","rollAction":"shield bash"}, reach 5 ft. Hit: x (2d3 + 3) Bludgeoning damage plus  (1D12) Force damage.

Force blast. Ranged Attack Roll: +4, range 120 ft. Hit: 22 (4d10) Force damage.

Slow (Recharge 5–6). The golem casts the Slow spell, requiring no spell components and using Constitution as the spellcasting ability (spell save DC 17).

SAP FROM EARTH: (2/day) (1D20):  

On a bonus action the golem slams his hands into the ground and drains the energy from the earth to restore health.  

Create pebble guards: At end of turn roll 1D6 to summon pebble guardians at cost of 10 hp. 

PEBBLE GUARDIANS

AC:13

HP:8

int: +2

attack: fist. 1D8+2. HIT: +3

Merge: pebble guardians get absorbed by ancient guardian for remaining HP.