About Kaagaz
Don’t use paper. Use Kaagaz.
"Yhorm" was supposed to be the games tutorial boss, but he was still called Gundyr, just with the current Yhorm model. The area was designed around Yhorm waking up from the coffin alongside you and he was a simple boss easing people into the game. He would re appear later with the glowing eyes and be much harder. Storm Ruler had nothing to do with him.

"Gundyr" as we know him was originally called Old King Oceiros and was in where Dragonfucker is right now. Dragonfucker being a post Bloodborne DLC change by C team to ape the Ludwig experience.

Untended Graves was actually the beginning of a cut level that went all the way to Soul of Cinder through a ruined firelink and lower wall area, filled with black knights to pay homeage to the original.

"Yhorm the Giant of the Profaned Capital" was actually originally using Wolnir's Model, and he was a gold obsessed mad skeleton optional boss and covenant leader of the Mound Makers.

Carthus Catacombs was originally accessed after Greatwood, where the alter is now, that was actually a doorway.

Smoldering Lake used to have path up to Irithyll starting from the large crossbow, and met up with the broken stair section where you fight the Alva invader. This is also why the Pontif Beast can appear either in the water or at the bridge, because originally there were 2 ways into Irithyll.

Abyss Watcher's led straight up to Irithyll's bridge area, Abyss Watcher's themselves being much much harder than they are now with more health and damage.

Deacon's of the Deep was originally a 2 phase and they had a cutscene and everything, aldritch would flow out of the coffin and the fight would involve circling around the cube.

The entire area in Smouldering Lake with the crossbow was actually a boss arena where you would fight a giant bat, and you could crash through the ground to avoid the boss, and then use the crossbow to wound it, a combination of Dragon God and Kalameet mechanics, then phase 2 would be the giant worm appears.

I actually know all that as fact but I have no physical proof what so ever because it was mostly, scrubbed, though I think the bat is probably still in the games files somewhere, I have no idea, also Gundyr's armour description still refers to it being the old kings armour afaik

There's more by the way. Twin Princes, infact, the entire lothric castle area was at night, and there were serpents with wings flying around instead. The Darksign Sun thing was only going to happen with the Untended Graves area, not lothric castle. The Pilgrim Butterflies weren't a thing.

There's a giant hole in the building where Twin Princes are. That's where Kaathe would fly in from in an encounter. It's hard to explain.

Also the Elder Prince had a totally different sword originally but the icon for the current one is the same as the old one, it was a big rusty slab thing. That was when the fight involved Kaathe.