Shapechanger. The Zac can use its action to polymorph into an object or back into its true, amorphous form. Its statistics are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies.

False Appearance (Object Form Only). While the Zac remains motionless, it is indistinguishable from an ordinary object.

Magic Net. The Zac can only be affected by one type of magical damage at any given time. All other magic deals 1 damage to it. The magic that can damage the Zac deals double damage. Choose which type they start being vulnerable to then roll randomly to determine after they are hit with the weakness type. Roll a D110, if the same damage type is rolled as they were already weak against is rolled again re-roll.

1. Acid
2. Cold
3. Fire
4. Force
5. Lightning
6. Necrotic
7. Poison 
8. Psychic
9. Radiant
10. Thunder

Resilient Body. Reduces all total damage dealt each round by 20.  

Rebirth. After being downed the Zac bleeds out holy water, this is special holy water and holds mystical and wondrous powers unknown to most everyone. Although, on a D6 roll in rounds the Zac regains 2d10 + 7 back in hit points. It immediately attacks the closes target in the church yard cemetery. 

Turn Immunity. Not fully construct not fully undead, a curious creature created in the early days of magic. The Zac is immune to all turn attempts, although it does take the Clerics level in un-mitigated damage.  

Multiattack. The Zac may make two slam attacks or two plank bash a round. 

Absorb. The Zac can absorb magic and be healed by the last Spell that hurt it, this only can occur once per a Magic Net effect. See Magic Net

Slam. Melee Weapon Attack: +6 to hit, reach 15 ft Radius  Area target. Hit: #23(5d12 + 5) Bludgeoning damage. 
The Church slams down on the ground all with in a 15 ft. Square are hit

Magic Barrage. Unleash a volley of magical energies the same damage type as what hurt the Zac, during Magic Net. Deals 20 damage, or 10 damage on a successful DC 12 Dexterity save, if targets failed the Strength save for Undead Grasp they do not get to make the Dexterity save. The Zac uses Undead Grasp before using this. 

Plank Bash. Melee Weapon Attack: +5 to hit, reach 15 ft.. Hit: 25 bludgeoning damage. Only does this if any targets are turned into rats and only attacks rats. Hits one target. If someone is a rat ZAC takes a Plank bash from the get go, then may take up to two plank bash attacks at the end of the following turns, until all the rats are dead. 

Undead Grasp. All players in a the graveyard of the church must make a DC 14 Strength Save or be Incapacitated .  The hands go away at the end of the turn. On a failure 

Swallowed (Only happens after taking 75 Hit points).

The ZAC Makes a slam attack, this attack requires a DC 14 Strength Save or be pushed back 15 ft. After which the ZAC begins to inhale sucking in all in a 120 ft. Cone.

Roll a D8 to identify the direct in which the cone is facing, The zac will always stop in a direction of a target. If the direction rolled has no target Turn the zac Counter clockwise if the number is even till the center of the cone is on a target. If the Roll is Odd turn the Zac clockwise till the cone is center on a target. A roll of 1 being North, and 3 being east.  

All targets in the Cone must make a DC 17 Strength Save or be moved by the following 
Failing by less than 5 - Half your movement speed
Failing by 5 - Your full movement speed 
Failing by 10 or more - 1.5 times your movement speed

Once the Zac has engulfed someone the it releases Necro Eyes equal to the result of 2D10. The Zac also turns to a magical stone that takes Zero damage from all sources, until it takes 50 damage from the swallowed person or 3 rounds have passed. 
The swallowed target makes attack rolls at Disadvantage but only needs an AC 10 to hit. The Zac does not remove the damage from his health. Any target in that Zac swallows takes 15 Necrotic damage at the begin of their turn.  

Necro eyes -  Ranged Weapon Attack: -- to hit, range 120 ft Target: One Target Per. Hit: # 2 (1d4 ) necrotic damage. 

You should evenly split the eyes up per each player. The eyes only have 1 hit point. AoE damage should remove 2 eyes per every 10 damage, for more difficulty you can do 1 eye per 10 damage. The necro eyes get to attack one target per an eye after each creatures turn in the imitative order. 

Noxious Breath. All in a 90 ft. sphere of the Zac takes, makes a DC 17 Wisdom Save Nothing happens on a successful save for status effects and half damage on damage. Otherwise roll a D6 for each player. 

1. Take 21 Poison Damage and you have the poison condition
2. Take 21 Necrotic Damage and receive half healing effects for two rounds 
3. You become silence for two rounds ( unable to use magic) 
4. You are turned into a Rat with 1 HP, any damage you take kills the rat and you are reverted back to your original form, but any damage over 1 hp carry's over. Last for two rounds
5. Confused roll a D6 on an even number attack an ally on odd attack your preferred target. This affect last for 2 rounds.
6. You are frightened for two rounds.

Nullify Magic (Necrotic Drain) Only happens after every 100 Hit points of damage. 

The Zac in a 200 ft. Sphere creates a necrotic Anti magical affect. No magic is able to be cast for 1 round. This resets the initiative regardless of where in the Initiative the round is in. As soon as the threshold is reached this effect happens. All targets must make a DC 15 Constitution save or take 24 Necrotic damage, half as much on a successful save. All damage dealt heals the Zac.

This only activates after reaching 200 Hit points, then 100 hit points. This restarts the round as soon as the Zac takes enough damage to put them at the thresholds, regardless of how much damage is done when the threshold is reached the Zac does not fall below the threshold, until after this effect happens.

Bone claw assault (only happens when ZAC reaches 20 Hit points). 
Melee Weapon Attack: +6 to hit, reach 20 ft. special. Hit: #24(4d12) Slashing damage.

The house sprouts 6 bone claws from the side of the first floor that reaches out to 20 ft.. These claws spin at a fast speed around the house dealing massive damage to those that dare lose focus. Anytime a target creature in range makes more than One action they are the target of an attack. If the target is hit they must succeed at a DC 17 Strength saving throw or be knocked prone or knocked back 15 ft. Targets avoid taking attacks if they only take one action, devoting the rest of the time avoiding the incoming attacks of the bone claws. 

Enter the description for how legendary actions work for your monster here.

Legendary Action Name (Costs # Actions). Enter the description for your legendary action.