Lava beasts are found within the Volcanic Mine on the Fossil Island Volcano. They attack players in the mine, and are weak to water spells, which they take double damage from.
It is recommended to ignore them and focus on mining the boulder, as Protect from Missiles will reduce their max hit to 1. Their attacks can damage multiple people at once, similar to chinchompas or barrage spells. The damage of the attack is calculated shortly before the projectile lands rather than when the attack animation starts, unlike most other monsters, meaning players have time to see their attacks coming and pray accordingly.