The Rewriter, Codex of Change

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Medium Aberration (shapechanger, stat-block manipulation), Neutral Evil

Armor Class 16 (natural armor)

Hit Points 102 (12d8+48)

Speed 30 ft.

STR 16 (+3)

DEX 14 (+2)

CON 18 (+4)

INT 10 (+0)

WIS 14 (+2)

CHA 8 (-1)

Saving Throws Con +8, Wis +6

Skills Stealth +6, Perception +4

Senses darkvision 60 ft., passive Perception 14

Languages Common

Challenge 9 (5,000 XP) Proficiency Bonus +4

Adaptive Form. The Rewriter can rewrite its own stat block mid-fight by using its Rewrite Form ability (3/Day). When it does, its form changes to Form B (Apex Form) or Form C (Crowned Form) for the specified duration, altering its AC, hit points, saves, and attacks. The exact numbers for each form are described in the form notes.

Keen Senses. The Rewriter has advantage on Wisdom (Perception) checks that rely on sight, hearing, or smell.

Actions

Multiattack. The Rewriter makes two Claw attacks and one Bite attack.

Claw. Melee weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 10 (2d6+3) slashing damage.

Bite. Melee weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 12 (2d8+3) piercing damage.

Rewrite Form (Recharge 3/Day). The Rewriter rewrites its stat block, switching to Form B (Apex Form) for 2 rounds or Form C (Crowned Form) for 1 round. In Form B, AC increases, HP rises, and its attacks deal more damage; in Form C, it gains a burst of disruptive abilities. The exact stats for Form B and Form C are described in the form notes.

Legendary Actions

The creature can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. The creature regains spent legendary actions at the start of its turn.

Detect. The creature makes a Wisdom (Perception) check.

Rewrite Switch (Costs 2 Actions). The Rewriter uses its form-altering ability to switch to the other form (Form A to Form B, or Form B to Form A).

Tentacle Lash. The Rewriter makes one Tentacle attack.

Environment Underdark

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Lore & Description

Appearance

A shifting, ink-black crystalline construct etched with blinking glyphs that rearrange themselves when viewed from different angles. Its core glows with pale runes that rearrange like pages turning in an unseen library. The Rewriter speaks in a chorus of whispers, its vowels constantly shifting into fresh syllables. It can bend the very rules that bind it, rewriting its own stat block mid-fight to shift into more dangerous forms. When forms change, its armor class, hit points, and the abilities it wields transform, forcing a party to abandon any pre-battle plan and improvise on the fly.

Behavior & Origins

In the ruins of a sunken archive, a sentient glyph called The Rewriter learned to bend the rules that bind it. Each battle becomes a draft in which it edits itself—gaining new powers, discarding old ones, and testing enemies with unpredictable shifts. Its hidden goal is to collect and guard a grammar of power that binds its shifting forms, revealing itself only when a foe proves complacent.

Monster Image

Generation Info

Original prompt:
"A monster that rewrites its own stat block mid-fight."

Created: Feb 2, 2026
Modified: May 22, 2026