Alson's Monsters are the creatures and minions who serve Alson Mestari and help him carry out his plans. They are used to track Matilda and Thomas, fight their enemies, gather information, and ultimately help Alson reclaim The Magic Heart.

Alson's monsters come in different forms and abilities, making them a constant threat throughout Matilda and Thomas's journey. Some are sent directly into battle, while others are used to spy on the heroes and report information back to Alson.

Their loyalty to Alson makes them dangerous enemies. They follow his orders and help him pursue Matilda wherever her quest takes her. The lead Slender, one of Alson's most trusted minions, is responsible for helping locate Matilda and Thomas and reporting their movements to Alson.

As Matilda collects more of The Magic Heart's power gemstones, Alson's monsters become an increasingly important part of his attempts to stop her.

Slenders are tall, skinny creatures with sharp claws, sharp fangs, and one red eye. Their best weapon is their claws. 

Arachnes are creatures that are half human, half spider. They also have red eyes and red fangs, but their best weapons are their spears.

Slithers are long, snake-like creatures with a human-like head. They slither around like snakes but their best weapon is their sharp red fangs.

The book where 'Alson's Monsters' appear in.