The Cup of Life from BBC Merlin

I've been brainstorming on what it would be like if BBC Merlin's Cup of Life existed in DnD as an artifact-level magic item. It would go something like this:

Healing. As an action, a creature can use a level ??? spell slot or pass a DC ??? Arcana check to conjure water in the Cup. The first creature to drink the conjured water as an action or bonus action receives ??? healing and the effects of the Greater Restoration spell. This effect does not work on undead or constructs.

Immortal Contract. A humanoid can spend 1 minute to shed blood into the Cup, receiving ??? necrotic damage that cannot be reduced in any way at the start of the minute. If the minute passes uninterrupted, their creature type changes to undead and they become immune to all damage types except radiant. Multiple creatures can gain this effect at once. While the Cup contains any blood shed in this way, its healing effect cannot be used. A creature can use an attack action to empty the Cup of all the blood it contains, causing all creatures to whom the blood belonged to die instantly.

What do you guys think? I tried to make it as similar as possible to the show except for not needing an extra ritual for the immortal contract. What numbers should go in those question marks for balance?

I like it a lot. Just a couple thoughts:

Having the immortal Contract deal damage is kind of pointless, since they then become immune to almost all damage. You should also put in some information about what happens if one creature is holding the cup and trying to prevent you from attacking it.

For the Healing, I'd suggest making it require "If the cup is filled with pure fresh water either from magically conjured water, an unspoiled natural source or fresh rain..." rather than just using a generic spellslot or Arcana check, because it adds the need to learn a magic-conjuring spell (there are quite a few to choose from) or seek out an appropriate source which IMO is more interesting than just spending a spell lot or making.a check. The amount of healing should be modest, the main benefit is the Greater Restoration, maybe ~30? but I'd make it really reliable rather than super dice dependent, so maybe something like 4d10+20?

Good points.

• I originally added the necrotic damage to be semi-symbolic, but I also think it adds a penalty to multiple interrupted attempts. Don't know how much that would come into play though, since the Immortal Contract is intended for villains like it was used in the show.
• Yeah I definitely need to add an "if the Cup is not being held" catch to the emptying action. There are enough rules in DnD around wresting an object out of someone else's grip, aren't there?
• I keep going back and forth about where the water has to come from and who can conjure it. In the show, they make it seem like any water drunk from the cup will work, but they also only show powerful spellcasters using it for healing, so it's up for interpretation. I thought of the arcana check because it's similar to the sphere of annihilation - technically anyone can use it, but they have to know their stuff. A friend suggested the generic spell slot. Defaulting to Create Water seems obvious but it's also pretty unfair to casters without access to that spell. Your suggestion of "unspoiled natural water" is a good idea, though it brings up a lot of questions about how to define that. Maybe holy water could be an option as well? I'd like to know if anyone else has ideas.