Along the pathway from the Archylte Steppe to the Mah’habara Subterra, you undoubtedly noticed the Behemoth King and Megistothorian battling one another along the cliff pathway.
The two enemies will not notice your party as they approach, which means that you can initiate a preemptive strike against these two enemies. The battle can still be fairly tough even with both of these enemies having 50% HP at the start of the battle, but there are some strategies you can employ to greatly reduce the time the battle takes.
Your primary objective after initiating the fight should be to Stagger and defeat the Behemoth King as quickly as you can when the fight begins. The Behemoth King, like other Behemoths, will eventually stand on two feet and recover all of its HP once its health drops too low, but if you Stagger it and use Launch to keep it up in the air, you can defeat it before it has a chance to trigger its second form.
Following the fight, you can save your game at the nearby Save Station and re-initiate the fight over and over again. Each time you defeat the pair of enemies you will gain 6,600 Crystogen Points (CP) and because of how quickly this can be done this ends up being an excellent farming area early on in the game to build up some CP.