I wonder whats wrong with the build I’m having. Can’t kill Lagon to save my life and I’m practically stuck for hours now at low mod level 85 monos. 
Dying is a problem, but it can also be that I’m not doing enough DPS, especially when it comes to Lagon and similar baddies.
Is the problem with lagon that you’re dying to the abilities it does?
Couple of things:
Cinder Song, your weapon is not particularly good unless you are going ignite, because the spell damage is very low and doesn’t justify the %inc dmg and extra projectiles. A mediocre rare wand appropiate for you level Dragonhorn or Crystal Wand will do massively more damage.
Your gear and stats are all over the place. I have the feeling you equipped a couple of exalted items just because you got them. But a decently rolled Rare will be better with affixes more aligned with your build. Your Body Armour and Relic are exalted, but the exalted affixes are not doing a lot for you.
Do you want to be a ward build or health build? Both are possible but you should choose.
If you want to be a health build you definitely should invest into the Sorcerer Tree and max out the Lavamancer Passive for leech.
If you are going full ward, get rid of all the health stuff on your gear that doesn’t do anything.
Also on the topic of Lagon, he is a very mechanical boss and you really just need to learn his mechanics and focus on dodging and not being greedy with the dps. You can do him without getting hit at all if you really try.
Yes, in phase 3. Phase 1 I can do, phase 2 is a joke anyway, but in phase 3 I ALWAYS die.
Ok, thanks, I based the build around this one, but decided to stick to fireballing for now:
That Cinder Song just sounded too good to be true, will go back to 70 / 75 monos now and replace it asap.
Thank you!
Didn’t decided between ward and health, yet… for now I guess I have to “go with the flow” and take what I get from loot.
So based on your gear, you shouldnt really be having trouble, imo. I feel like the problem you have is just the mechanics, monolith lagon is like, the first real ‘oh no’ moment, and really the point the game goes ‘we have one shots, you need to learn the mechanics and pattern of them, and work out how to avoid getting hit’
While you could have more damage like, realistically that isn’t the actual problem, and will more just seek to reduce the amount of times you can make a mistake. If you’re getting to phase 3 fine, then dps wouldnt be what i’d focus on personally.
Most important things for Lagon are to dodge his breath attack and his big circle AOE.
The advice I read was for ranged builds to stand roughly in the middle of the platform, ideally at the top (closest to lagon). Then when he does his breath weapon, you can run to either side to dodge. And if he does his big circular AOE, same thing, just run to either side.
In phase 3 you’ll have to move up and down to try to dodge some of the waves, you should be able to tank some of them, but dodging will help reduce the damage you take.
Another tip is to do Echoes that give bonuses to Rare enemies before attempting Lagon. There’s no rare enemies, so those bonuses don’t affect the fight. Definitely don’t try to kill him with something like ‘enemies deal increased elemental damage’ active.
Good tips, but I really had to laugh at your first paragraph 
So Lagon is breathing through his Eye? 
Lagon’s eye is charging red before this attack and then he does the beam with his eye, just in chase you never noticed 
Lol nope, I just see a howling gale coming out of him and try not to die.
I can sympathise alot with the OP. It took me maybe 10 goes to finally take him down, and it was simply a case of learning the mechanics better.
I do feel he’s overtuned for the level you meet him at. I went on to fight other monoliths bosses, significantly higher level than me and none of them gave me the same problems as Lagon.
I also found it hugely helpful to use a skill like lunge with the right node that can kill enemies below 15% health. That can shorten boss fights a fair bit.