If you want some tips on how to do the lagon fight I made guides for all the boss fights a long time ago.
Some of the info regarding enemy modifiers is outdated, but mechanically the bosses are still the same, except lagon with the new tentacles.
But the strategy and his attacks are still valid.
What also has a great impact on the boss difficulty are enemy modifiers. Do you take them into consideration before starting a boss fight?
In case you don’t, you can play accordingly and let them drop of using Beacons, Vessels or Quest Echoes. Or you pick very carefully a few echoes before you reach enough stability for the boss