Clockwork Guardian

Clockwork Heart When the clockwork guardian is reduced to 0 hit points, it can make a DC 10 Constitution saving throw regaining 1 hit point on a success. For each success, the DC increases by 5. The DC resets after a long or short rest.

Construct Nature The clockwork guardian does not need to eat, breath, or sleep

Defender When the clockwork guardian hits a creature with an attack, that creature suffers disadvantage on all attack rolls against creatures other than the clockwork guardian until the end of its next turn.

Energy Cascade When the clockwork guardian is hit with a critical hit, it takes an additional 9(2d8) lightning damage on top of the critical damage.

False Appearance While motionless, the clockwork guardian is indistinguishable from a statue.

Gear Jam When the clockwork guardian is hit with a critical hit, it must succeed a Constitution saving throw equal to half of the damage dealt (minimum 10) or be stunned until the end of its next turn.

Immutable Form The clockwork guardian is immune to any effects or magic that would alter its form.

Internal Clock The clockwork guardian has advantage on initiative checks.

Overclock When the clockwork guardian hits a creature with a critical hit, it can make an additional weapon attack as part of that action. It an only benefit from this feature once a turn.

Rewind(Recharge 5-6) The clockwork guardian can take an additional turn at initiative count -10 (minimum of 1) for one round.

Spellcasting. The [monster name] is a #-level spellcaster. Its spellcasting ability is [ability score] (spell save DC #, +# to hit with spell attacks). The [monster name] has following [class name] spells prepared:
Cantrips (at will): [spell name], [spell name] 
1st level (# slots): [spell name], [spell name] 

Multiattack. The clockwork guardian can make two attacks on its turn. These attacks can be its choice of its Gearglaive or Charged Gear Launcher.

Charged Gear Glaive. Melee Weapon Attack: +7 to hit, reach 10 ft., 1 target. Hit: 7(2d4 + 2) bludgeoning damage + 5 (2d4) slashing damage + 9(2d8) lighting damage. Upon a hit, the target cannot take reactions until the end of its next turn. 

Gear Launcher. Ranged Weapon Attack: +7 to hit, range 60/120 ft., 1 target. Hit: 15(4d4 + 5) slashing damage + 9(2d8) lightning damage. On a hit, the next attack until the end of its next turn against that creature deals an additional 9(2d8) lighning damage.

Gear Shift. The clockwork guardian can use its bonus action to either Dash or make a single weapon attack of its choice.

Reactive. The clockwork guardian can take a reaction at the end of each of its turns.