Sundered

To access the true ending boss you need to find and corrupt all the seven elder shards, so basically it will be your final task, once you kill the 3rd main boss in the game and corrupt all the shards a portal will open in the shrine,but before entering the portal you must choose your perks wisely, from my experience the shield piercer perk is mandatory so you'll not have much trouble with the light form of Eshe, for the other perks it's up to your play style but i highly recommend perks that add critical hit chance and critical hit damage so you will have less trouble while fighting the final form of the ending boss
Speaking of boss, the fight is divided into 3 parts : the first one is 3 waves of enemies from the game which is fairly simple and straightforward, once you dispatch the last wave you'll hit the only checkpoint available in the fight.
The second part consists of fighting a light form of Eshe, she's very fast and hits hard especially with the cannon, so my advice is stick to her mostly so she can't use the cannon, try to lure her into the corner and keep mashing the square button so you can inflict a lot of damage, and here's why i insisted on the shield piercer perk cause she has a big shield that won't go easily. Once you kill her you'll face the real final boss : Humanity, which is basically a fucking moving shard with a monster guarding it.
As for the other bosses you need to hit the moving shard so don't waste your time hitting the monster cause he's invulnerable.
The fight with humanity is divided into 2 parts : the first part consists of the monster releasing a Web of spikes which is annoying as hell and he'll keep teleporting everytime he unleashes the spikes, be aware though that the fight arena is annoying as fuck cause you have little platforms to stand on so you should rely mostly on your grappling hook. The second attack is some sort of fireball with spikes, be cautious though cause the boss this time will be teleporting vertically and he hurts so bad especially with presence of the fucking spikes, my advice here is to abuse your teleporting skill to avoid his damage and also avoid the spikes.
The second part of the fight will start once you have lowered the boss health bar under 50%, he will go ape shit and he will unleash a lot of spikes and fireballs so try to be on your toes and hit the shard as fast as you can. Remember your saving grace here is your teleporting skill so use it when necessary. Once you lower the boss health bar to zero the trophy will unlock few seconds after. Good luck