Weave Eater

Weave Nibblers. The Weave Eater's body is covered with the exposed heads of thousands of its offspring. These offspring hatch randomly. While still attached to the main body, the Nibblers act as the beast's protectors.

Anti-Magic Defense. As the Weave Eater can only digest raw Weave magic, each Nibbler head produces a 300-ft cone of Anti-magic Field at all times while attached to the body.

Limited Senses. The beast does have eyes, ears, and a nose, but it is so vast that it can't perceive things of size Large or smaller by regular means. However, it does gain true knowledge of the current position of any caster that deals damage to it directly with a spell. 

Independent Nibblers. Once awoken, Nibbler heads gain an initiative of 16 and act independently of the main body. 

Weave-Tearing Beam. All Nibbler heads with targets attack with a single, silver ray with a 5ft radius.
Save by rolling your spellcasting score, no modifiers added. 
A player can take a number of hits from the Beam equal to their spellcasting modifier, after which they are unable to cast magic for 1d4 rounds.  
Players with an attuned Weave Focus are immune to this attack. 

Stomp. 3-turn Melee Attack:  On the first turn, the Eater raises 1 mighty hand. In water, the surface rushes toward the center in a 50-mile radius and deposits anything caught in a vortex that reaches the bottom of the body of water. 
On the 2nd turn, the Eater aims its hand. Wisdom save 16 to know where it will land. 
3rd turn, it smashes. 10d20 damage. Max range of 70 miles from the shoulder, 225 deg from the side. Pushes away a 50-mile radius of water. 
The Eater will only attempt a Stomp if no hatched Nibblers are in combat. 

Hatch Nibbler. The Eater may use an action to funnel Weave energy into 1d6 of its hatchlings, causing them to grow and eject themselves from the main body. See the separate Weave Nibbler page. 

Font of Magic. Whenever a Nibbler head drops to 0HP, a fountain of magic that the Eater was digesting spews forth in the form of a Wish spell (duplicating any 8th-level or below spell) or Wild Magic Surge targeted on the person who dealt the final blow. 

The GM should use a random spell generator set to 8th-level or below or consult a d10,000Wild Magic Surge table and apply the effect appropriately. 

Target Selection. The Nibbler heads are arranged in 3 basic alternating rows along the Eater's left and right sides, forming a brick pattern.
Whenever a head is attacked with a damage-dealing magic spell, its reaction, along with every immediately adjacent head (maximum of 6 additional heads), is to switch its target to the attacker. The heads cannot target anyone directly above, below, or on the other side of the Eater. 
Approximately 100 heads are in each row, for a total of 600 potential Nibblers. 

Adjust. Every 3rd round when the Eater is not performing Stomp, the Eater can move one of its two arms anywhere within its 100 mile, 225 deg range, causing a wave equivalent to a Tidal Wave spell in the initial direction of movement. 

Finale. Once combat begins, the Eater's efforts start to work up its appetite.

On round 300, the main body begins preparing its Weave-Destroying Laser.
On round 600 (after an hour of combat) the Eater fires its Weave-Destroying Laser through the center of the Plane it occupies, permanently disrupting anyone on the Plane's ability to use Magic, even if they are holding an attuned Weave Focus. This beam takes 4 rounds to complete its path.
After this, the Eater instantly disappears and re-appears a few miles above the start of the beam path (1 turn). Then it charges toward the center (1 turn til contact). Finally, it tears through anything and everything as it consumes the torn Weave all the way to the Center of the Plane. This destroys a regular planet. After it does this, it rests for 300 years.