Agonizer 9000 is a pain (heh) because he has limited crit spots - if you break them too quickly, you’re stuck doing regular shots. There isn’t much of a counter to this, other than having high dps weapons that don’t rely too heavily on crits.
As for hints for the fight, it really depends on what vault hunter you are playing, what difficulty, and what level you are. Still, I’ll try to give some general tips. Apologies if any of this comes off as patronizing, but with out more detailed information, the best I can do is general information.
First, get a corrosive weapon. The vast majority of the fight you are dealing with armor, and corrosive weapons make a big difference. If you are lower level, don’t worry about replacing a lower level purple with a higher level blue. Sometimes a green will even outclass a purple if it is higher level and the right kind of weapon for your build. Where to find one depends on your level (at 50, just farm an easier boss, otherwise, check vendors including Earl). Also make sure your shield is up to date. At lower level, Earl’s is again a good place to look. For leveling, I like the ones that drop bonus shields/health on taking damage and the ones that give damage resistance on taking damage.
Second, learn his attacks, and make sure to keep moving. A lot of them can be avoided if you keep running around him in a circle. You’ll also be able to get to the large crit spot in his back if you do this. The sawblade that spins around him will sometimes go high, in which case you duck, and sometimes go low, in which case jump. Keep moving when the masher attack shows up.
Finally, for dealing with the floor, you have to learn the patterns, and move quickly. He will either light the floor on fire in a circular pattern, or going from the center outwards. There should always be at least some safe space to move to. The floor won’t hurt you when it glows, but obviously it will be on fire soon so find a safe place. Sometimes you can avoid the burning floor by climbing on the little walls that show up during the fight.
tldr; Learn how he telegraphs his attacks, keep moving, get a corrosive weapon and a better shield. If you give us more info about your level/class/build, we can get give you more specifics.