Popular Dark Souls modder and explorer ZullieTheWitch has figured out a way to play the RPG as any of the enemies or NPCs. So yes, that means you can play as a Bonewheel, and it means you can play as a Crystal Golem. But more importantly, it means it's possible to play as a Crystal Lizard (see picture above).
...and by possible, I mean it's possible if you want to fiddle around with the game yourself. This isn't the result of a publicly released mod that you can download, in other words – it's just the result of ZullieTheWitch's code diving.
There's a bunch more to peruse over on Zullie The Witch's Twitter account. The Dark Souls specialist has also thoroughly dissected the recent Remaster for unused equipment and enemies over on YouTube.