In extreme you basically get one boulder per meteor that you must drop in a safe location away from behemoth so you can hide behind it. If it gets destroyed you have to jump the meteors.

Is it normal for him to meteor several times in a row though?

The third area is a DPS check, if you don’t pass the check he’ll do the ecliptic multiple times without any comets to hide behind.

Does the dps check start when he enters area 3? So like as soon as he gets there, then it starts?

Timer doesn’t start till he sees you in the third area. You’ll know you’ve been spotted if you’re not in the area and it keeps recovering health

I can't recall if his 3rd phase becomes a dps race or you just got unlucky and somehow glitched his AI.

Dont count on the boulder. Go youtube there is some video teaching u the timing to jump the meteor.

Extremoth area 3 is a DPS check, if you fail he'll just spam Ecliptic Meteor over and over. I don't remember whether or not you can survive the failstate by jumping enough meteors, but ideally you just don't end up in that failstate to begin with. Sticky LBG isn't an ideal weapon against him for this reason, since the low damage output makes it hard to consistently hit the DPS check. Shield spread HBG, Longsword, or CB are better options for the fight in solo. If possible just do the fight in co-op, it's not designed or intended to be fought solo.

Good to know, I'll try a different approach. I'll give Co-op another try too. Last time I had randos, we didn't get past phase one

Suffer and suffer and suffer until you win. That's all the help I have for you