¶ Why Monsters?
Because the edges of the map get less traffic, they're safer. The purpose of monsters is to reward Pawns who actively fight in the middle of the arena.
¶ How to Kill a Monster
Monsters are only directly affected by Pawn attacks. Items, Styles, nor Status can damage nor interact with them. Effects that increase an attack's damage, like getting Drunk from a Flask, or charging up Mighty do not apply their multipliers (and won't use charges), but the base damage of the attack will still apply. Despite this, some effects like Berserk can help with killing Monsters because the style increases the rate of attacks, not their damage.
¶ Monster Peculiarities
Monsters have no def and thus if they do take damage, they take that amount in full. Hitting a monster do not generate style charges. Single-target attacks are consumed when they hit monsters. When monsters combine, they heal to full.
¶ Worm 
• A worm spawns every 30.0 / pawnCount seconds.
• Worms have 25 hp and last until killed or combined.
• Killing a worm heals the attacker for 1% of their max hp.
• Three worms automatically combine into a snake.
¶ Snake 
• Snakes have 125 hp and last until killed or combined.
• Killing a snake heals the attacker for 5% of their max hp.
• Three snakes automatically combine into a fiend.
¶ Fiend 
• Fiends have 500 hp and last until killed.
• Killing a fiend heals the attacker for 25% of their max hp.