I had a rough time with him in normal mono on my falconer before I transitioned to ballistas. Ended up going up the left side path to empower and then came back to kill him once I had better gear/DPS. The fight feels like more of a DPS check than anything. My DPS was lacking and I’d eventually eat it while trying to dodge the lateral waves while trying to kill him.
Everything in Lagon’s fight is telegraphed, it’s literally a learning the mechanics check. There’s less RNG involves than with any other boss. Getting hit by a wave or two in the potion resupply phase shouldn’t kill you unless you’re at an absurd corruption level, and if you’re at an absurd corruption level you should be seasoned enough to avoid them (and have the tools to do so, i.e. movement speed, movement skills).
I was about to say that very thing.
The primary thing that is one shotting players is the beam sweep. When you see lagon (in the background), open his eye and it turns red, he will sway to one side and start sweeping with the laser. If you are reacting to the laser and not Lagon BEFORE he fires the laser, the telegraph is impossible to dodge since it comes out immediately.
There’s also an absurdly cheap cheese you can do for this too. Simply hit one of the two tentacles while staying towards the middle. When you see lagon sway to start his beam, simply move to the edge or to the other tentacle. Since you started towards the middle, he will only sweep from the middle to the tentacle you were fighting. So the wall-edge of the tentacle you were fighting or anywhere near the opposite tentacle are safe spots.
If you are on top of the tentacle or near the wall-edge before Lagon starts his beam, he will sweep starting from that side to the wall-edge, which will trap you if you move to the wall-edge instead of the opposite side.
Im in my First walkthrough and playing HC
Lagon is next with my necro and with my Pala.
Saw this thread and have to admit I get a Bit anxiois 
Resistances are capped, Bit IThink I will Go monos First for a few Upgrades.
Stay away from the eye. That’s it. He looks left, you go right. He looks right, you go left. Second phase run around the outside opposite the waves. That’s it. Go back up and stay away from his eye. Don’t even look at your own character, look at his eye and attack the tentacle he isn’t looking toward. Killed him in campaign and in monoliths 3 times with one death. On a Pally with no ward. 
2 Likes
Lagon is definitely a gear check / skill check.
My deaths have always been on phase 1 mostly due to eye beam.
In phase 2, I do get hit by waves a lot, but my leech is fairly high and I just keep attacking stuff to keep health up.
This. It’s a recipe for success. Take your time, and be mindful of the crossing waves in the final phase.
The last two story bosses used to both be gear checks that required you to pay attention and play. They are now complete face rolls with no skill needed to beat them. Maybe this isn’t the game for you. Candy Crush seems like more of your speed.