Really getting Magmasaur eggs are super easy because unlike the Wyverns and Rock Drake, they are limited to the ground. All you need to bring is a crossbow and grappling hooks, maybe even a climbing pick! Then descend slowly and yoink one out of its nest, then quickly pull yourself up and get back to your base and BOOM You got a Magmasaur. Do be carful of the eruptions thou, that happen randomly.
Magmasaur is able to destroy ALL STRUCTURES utilizing its searing spit. While it is a walking forge it produces metal at the same rate as a refining forge. You can use the jump button to taunt other creatures and when holding searing spit use crouch to erupt. (This attack pushes creatures back and leaves magma everywhere) it is breedable in lava. Hope this helped