Magmorax

Located in Molten Crucible, Aberrus, the Shadowed Crucible (Raid). Tameable in Normal mode, so you don't need to enter a higher difficulty if you don't want to. To reach Magmorax you have to defeat the first six bosses of the raid: the first is Kazzara, followed by Amalgamation Chamber and Forgotten Experiments on the left side of the raid, and Assault of the Zaqali and Rashok, the Elder on the right (it doesn't matter if you go left or right first). The doors to Zskarn (centre, top) will now be unlocked. After defeating Zskarn you can drop down through a slot in the balcony floor to the magma below. Kill all the Voracious Magma Worms surrounding the central platform to activate Magmorax. Note that this boss will respawn very soon after taming, so you can tame another, or kill it! It's possible that using the raid skip will prevent you reaching this boss.