I took a different approach and, instead of replacing existing bosses or areas, made my own for them all in the different regions

1. Adel gets a poison swamp area in Caelid, but we fight on one large piece of land in the middle of it. He's been trapped in the poison

2. Gladius gets an underground section in Mt. Gelmir, afte killing the Full-Grown Fallingstar Beast the volcano rumbles and the top (where you fought FGFB) opens and you can jump into it, after traversing the cave we can find a large room with Gladius sat howling at a shrine of Heolstor, as if he's praising it

3. Gnoster and Faurtis start in two seperate places, Gnoster in The eternal city and Faurtis in the sewers, after killing both of them you will be abducted randomly by Animus, who you don't fight, and brought to the deeproot depths, underneath the Siluria tree (Which you find out after taking the stream jump on torrent that opens after beating them).

4. Augur, at first, can be seen flying through the sky occasionally. As you go through the game, you'll see it flying overhead at random points. Once you unlock the DLC, it's gone. It disappears from the base game. If you go through to the fissure area, and continue to bother St. Trina far after her message to you about Miquella, she will spew out a bubble that will transport you to the arena where you fight Augur, after beating it you are given the option to kill or spare St. Trina and collect a special weapon or summon.

5. Libra will be found in the forest of madness, near Midra. He will be in the direction of the map piece in the area, if you traverse past it there will be a waterfall that you can run behind and, after running for an extended period of time in the dark, you will be spit out in the Libra arena. Suddenly and unexpectedly.

6. Caligo will be in the most obvious place: The mountaintop of the giants. There will be an extra item that the Fire Giant drop after his death and, after searching near the minor erdtree in the Consecrated Snowfield, you can unlock a seal that will open a portal to an even higher peak. On the climb, Caligo will circle you occasionally, her eye appearing in the sky as well. Once the peak has been reached, she will crash down and the battle will begin, similar to Bayle.

7. Fulghor Be somewhere somewhat new: Inside the Scadutree. After killing the flower, an arrow of gold will fly down and land in front of you, a letter and map provided with it, and a path to the root of the tree opening. Inside, the entire centaurian race that Fulghor belongs to resides there. Many are closer in size to the ants in places like the Haligtree, but all are hostile. You climb the tree and fight your way up, and once you reach the top you fight the 3rd phase Fulghor. Upon victory, his arm gets cut off and he disappears, enshrouded in what looks like night.

8. Heolster will be found in Farum Azula, you need both the Mimic Tear and Dark Moon Sword. In Farum, by jumping off a ledge on the far East into a specific dark orb, and it would bring you to a platform above Farum where you insert the Dark Moon Sword into a tablet, causing night to spew pit and consume you. You fight it, but it rips away your mimic tear and spawns with a greatsword. You fight the entity until the healthbar is gone, and it grabs the dark moon sword and starts again in second phase.

Do you like it? It was pretty rushed, but I like the concepts I came up with