Core of the Tower

The wandering tower is a truly ancient mimic, one which has lasted for centuries or millennia. It has grown to incredible size, eventually so large its body is too clunky and awkward to move and has been adapted into a full building that the mimic can reshape over hours of time. Much more malevolent than lesser mimics, it hunts for humanoids specifically, using them as the basis for future mirror mimics. Once it lures in travellers it waits until they are vulnerable, at which point it attacks, unleashing everything onto its meal. Its central core moves in, covered in eyes, pseudopods and mouths, and the walls themselves start lashing out with grasping claws and acid dripping tendrils, while the doors slam shut.

Shelter from the Storm: According to legend, when the armies of evil encircled Gardmore Abbey, the abbey’s paladins entrusted a messenger with a map indicating the locations of their greatest artifacts and begged him to deliver it to the emperor. The messenger broke through enemy lines and sped toward the heart of Nerath. But an evening thunderstorm flooded the King’s Road, preventing the messenger from traveling farther.

In the midst of the storm, the messenger spied a thatched two-story inn with ravens nesting in the eaves. He had never noticed it before, though he had traveled the road many times.

“Here may you find all you desire,” said the rotund proprietor, who greeted him at the door.

That night the messenger sank deep into the inn’s soft bed, and he was never seen or heard from again. The map to the paladins’ artifacts disappeared. Of the inn, no sign was ever found.

Holy Sanctuary: At the dawn of Nerath, noble knights of Pelor quested to find the Sunspire, a legendary amber tower where the sun’s daughter dwelled. In those days, it was said that the true knight who found the Sunspire would earn the favor ofPelor and receive
the bright lady’s hand in marriage. But no one had ever seen the Sunspire, for it was said to fade away like day before the coming night.

One dark day when ravens filled the sky, a brave knight came upon a tall amber tower where a goldenhaired lady sang from a high window. She greeted the knight, pronouncing him the champion of the quest.

“Here may you find all you desire,” she said, and she beckoned him inside.

The knight entered the tower and was never heard from again.

Originally from the 4e Monster Vault: Threats to the Nentir Vale. This post came out a week ago on my Patreon. If you want to get access to all my monster conversions early, as well as access to my premade adventures and other material I’m working on, consider backing me there!

5th Edition

Core of the Tower
Huge aberration, neutral evil
Armor Class 18 (natural armor)
Hit Points 216 (16d12 + 112)
Speed 30 ft.
Str 23 (+6) Dex 14 (+2) Con 24 (+7) Int 16 (+3) Wis 17 (+3) Cha 18 (+4)
Skills Stealth +7
Damage Resistances acid
Condition Immunities charmed, prone
Senses darkvision 120 ft., tremorsense 50 ft. passive Perception 13
Languages Common, Deep Speech
Challenge 14 (11500 XP)
Grappler. The core has advantage on attack rolls against any creature grappled by it.
Legendary Resistance (3/Day). If the core fails a saving throw, it can choose to succeed instead.
One With The Tower. The core cannot leave its lair, and is immune to any effect that would transport it outside its lair. The core can move through the walls of its lair as if they were difficult terrain, and can end its turn inside the walls. It can’t attack through walls.
Undaunted. If the core would be stunned, it instead halves its speed and has disadvantage on attack rolls and Strength and Dexterity saving throws for the duration it would be stunned.
Actions
Multiattack. The core makes two attacks, only one of which can be a Bite.
Bite. Melee Weapon Attack: +11 to hit, reach 5 ft., one target the core is grappling. Hit: 39 (6d10+6) piercing damage plus 18 (4d8) acid damage.
Pseudopod. Melee Weapon Attack: +11 to hit, reach 15 ft., one target. Hit: 22 (3d10+6) bludgeoning damage and the target is grabbed (escape DC 15). Ability checks made to escape this grapple have disadvantage.
Shapechange. The core can polymorph into a Large or Huge 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. While the core is motionless in object form, it is indistinguishable from an ordinary object.

The Wandering Tower
The wandering tower brings its lair with it, crafting it into a useful guise to lure in prey. Over the course of 6 hours, the tower can reshape its lair, transforming it into a building up to 1,000 feet long and wide, and a maximum of 3 stories tall. The building doesn’t have a basement. When the building is smaller than 30 feet long and wide and only one story tall, it is able to move at the core’s speed, crawling along to a new location. The lair must always be larger than the core. The walls of the lair are part of the core’s body; a 10 foot by 10 foot section has AC 16, 50 hp, resistance to acid damage, and immunity to psychic damage. Damage done to the walls does no damage to the core, and the walls can be repaired or replaced by the core as a lair action.

Lair Actions 
On initiative count 20 (losing initiative ties), the core takes a lair action to cause one of the following effects; the core can’t use the same effect two rounds in a row.

• The core can create, destroy, or restore to full health five 10 foot by 10 foot sections of wall anywhere within its lair. If newly created walls completely close in an area, it must also create a door leading into that new room. The door may be hidden (requiring a successful DC 20 Wisdom (Perception) or Intelligence (Investigation) check to find), locked (requiring a successful DC 20 Dexterity check using thieves’ tools to unlock), or jammed (requiring a successful DC 20 Strength (Athletics) check to force open) at the core’s choice.
• The floor ripples in a 25 foot radius centered at a point within its lair. Each creature standing on the ground in that area must succeed on a DC 20 Dexterity saving throw or fall prone.
• The core turns one 10 foot by 10 foot section of wall within its lair into Living Wall. Living wall is distinguishable from regular wall. The core can’t create more than four sections of living wall at any time. If it creates an additional section when it already has 4 sections, one previously created section must be turned back into regular wall. On initiative count 20 each round, the core may make the following attack out of any section of living wall:
Lashing Tendrils. Melee Weapon Attack: +7 to hit, reach 15 feet, one target. Hit: 9 (1d10+4) bludgeoning damage, and the target is grappled and pulled until it is within 5 feet of the section of wall that attacked it. Until this grapple ends, the target is restrained and takes 5 (1d10) acid damage at the end of each of its turns. Each section of wall can only grapple one target at a time.

13th Age

Core of the Tower 
Huge 8th level wrecker [aberration] 
Initiative: +11
Slam +13 vs. AC (1d3 attacks; each against a different nearby enemy) – 50 damage
Natural Even Hit: The target pops free from each enemy and moves next to the core, which engages and grabs it. The core can grab any number of enemies simultaneously.
Natural Odd Hit: The target pops free from each enemy and loses its next move action.
Maw of Doom +17 vs. AC (one enemy it’s grabbing; includes +4 grab bonus) – 50 acid damage.
Quick Use: This ability only requires a quick action (once per round) to use.
C: Rippling Architecture +13 vs. PD (1d4+2 nearby enemies) – 15 damage and the target loses its next move action
Limited Use: 1/battle, as a quick action, but recharges when the core is staggered.
One With The Tower: The core can’t leave the tower, and it is immune to any effect that would transport it outside the tower.
No Exit: Once per round, as quick action, the core creates a jammed shut door blocking off a room and also locking any creatures in that room from reaching or attacking the core. A DC 25 skill check made as an action can force the door open.
Shapeshift: The core can disguise itself as a regular object. Outside of combat, a character must make a successful DC 35 skill check to identify the core as a creature. At the start of combat when the characters aren’t aware of the core, they must succeed on a DC 25 skill check to avoid a surprise round.
Undaunted: If the core is stunned, it is instead dazed for the same duration. It is immune to being confused.
Resist Acid 14+.
AC 23 PD 21 MD 20 HP 430