I've also thought about modding the lamb into DST. I'll share what I had in mind and you decide what you feel like doing with it, see these as suggestions. I wish you the best of luck with this mod and I will definitely try it when I play DST again.

I imagine him being a multiplayer focused character 'cus cult leader.
The lamb can create a statue of himself where any player can pray to at the cost of a lot of sanity, a sanity risk for their great cult leader. Each prayer generates devotion that the lamb can collect (the lamb can also pray so it's possible to get devotion when alone).
He starts out weak and each upgrade to the statue would increase the lamb's stats (the code of Wurt gaining stats when there's a Merm king could be useful), these upgrades become increasingly more expensive, requiring rarer materials and more devotion.
The lamb can create cult clothing that survivors can wear, these give a little sanity that is increased if a lamb is nearby. Necklaces are also something he can make for them with various effects like the Feathered Necklace increasing speed or the Moon Necklace negating the sanity drain of night.
The lamb will be able to create weapons and spells with devotion and other materials, the durability can be refilled with devotion.
Unfortunately the crown is the only thing the lamb can wear on his head, even if the crown is currently his weapon. This is a big drawback but luckily the crown has its own benefits that become stronger the better the statue is.
Of course the lamb can also make a book of blessing which when read will bless nearby players for slight sanity regen for a while.
Lastly the lamb can create a demonic circle where sacrifices can be made. Any player can kill themselves on it to generate a lot of devotion for the lamb and drop a heart for the lamb to eat. This heart rots very fast, it gives stronger health regen than jellybeans but drops sanity when eaten. If the heart is stale or spoiled, the health regen won’t last as long. The sacrificed player will have a guaranteed hp penalty of -75% hp no matter how they are revived and they cannot be sacrificed while they have a hp penalty. The freshness of the heart and amount of devotion is dependent on the player's hp, so players that sacrifice themselves when almost dead won't be as good as a player with full hp.

Maybe we should add to him the ability to tame some creatures into his cult and let's say in a circle it will be possible to make sacrifices to both players and kill creatures there?

P.S Sorry for small comment,I saw late that there are only big comments here

Tbh all you said is great and perfect just make sure you make the moon necklaces better like for 2 days night vision and drains hunger. and being able to interact with player's in a special way like blessing. Also adding the gauntlets they have more attack speed and hit harder on the 3rd hit :)

well, kevinator did very good and perfect suggestion, only thing i will add is posibillity to get npc cultists(idk,summon or find somewhere on the map,(one per world while it's not recruited,and 50 while it is),and you can tell to him to jobs from original game like getting rock's,wood,and pray)

he could do rituals every full/new moon like spawning food maxing stats or pausing hunger drain

A few suggestions from multiple people...
- Add custom sound to match "Baa" while still keeping the textless description of things around is a good touch.
- Animation for being hit is currently off like Lambert is enjoying being hit somehow.
- Add a ghost sprite, a floating crown. Perhaps instead of the typical ghost haunting using white silhouette, use black mix with red instead to match of the crown. This is truly needed since respawning is hard without ANY silhouette.

The characters in Cult of the Lamb, including The Lamb themselves, DO have dialogue, so I'd go with making The Lamb's interactions & inspection text demonic but goofy. That would show both The Lamb's own childlike innocence & the demonic influence of The One Who Waits, which affects them throughout the game. As such, demonic-but-goofy dialogue would be fitting for the lamb.

not sure if still updating this mod, but would be cool if you could get the fleece armor to work with extra equip slots
also would be cool if they could craft the crown into other tools or weapons and maybe as well upgrade them as you defeat certain bosses and progress through the game