Uncommon, 5000 gp

Quote from MonkeyManDan242 >>

Quote from Silverwave21 >>

Twice before the start of your next turn

 "If you take any damage while you have 0 hit points, you suffer a death saving throw failure. If the damage is from a critical hit, you suffer two failures instead. If the damage equals or exceeds your hit point maximum, you suffer instant death."

So three regular hits, or two crits, or one massive hit that does more than your maximum HP.

 Unconscious
• An unconscious creature is incapacitated (see the condition), can’t move or speak, and is unaware of its surroundings
• The creature drops whatever it’s holding and falls prone.
• The creature automatically fails Strength and Dexterity saving throws.
• Attack rolls against the creature have advantage.
• Any attack that hits the creature is a critical hit if the attacker is within 5 feet of the creature.

In a situation where you are not alone no one would try killing you while they know that you are downed and not getting up for 1d4 hours.
Once taken care of any other threats even a Ranged Creature can walk up to you to attack you unarmed in melee dealing guaranteed crits on a attack, so in 99% of times when you die because you got attacked while wearing this it's because you got crit twice.

Fact. We needed a mobile tank in the party, so I built a hill dwarf monk with high Con and the Dwarven Fortitude feat. In a pinch, he could use Patient Defense and stick out a tough fight. Then on a random loot role, I got this bad boy. OMG. On a good role, I'm 20+ hp up with the benefits of a dodge action. Combined with Tasha's Cauldron optional rules, I can use Quickened Healing out of combat to top off, and save those precious hit dice combined with the Periapt of Wound Closure for heals that make our bard's healing word go limp.

This combined with the Durable feat is OP.  Take notice, artificers.

This on a zealot barbarian...

Amulet of Plot Armor???

Just as a note...

This automatically stabilizes you at the start of your turn - that pack of wolves munching on the newly downed wizard inflicts two failed death saves with each attack. As a reminder about the condition, see: https://www.dndbeyond.com/sources/phb/appendix-a-conditions#Unconscious

Why?

Because the unconscious condition says that attacks are at advantage - in this case, we have a specific rule and a general rule (the prone condition, the incapacitated condition) and so we take the specific rule over the general rule, and it's intended that all attacks have advantage not just melee. Otherwise simply referencing the two conditions that give melee advantage would be sufficient, and we wouldn't need a separate bullet point with the broader "attacks" category.

Any melee attack within 5 feet is an automatic critical hit, costing two death save failures. You just need three death fails before the start of the player's next turn - and so the wolves can get that easily on most downed players.  You can play with this real quick with theory craft with a few creatures - the majority of creatures will have no problem with executing the downed player via standard attacks.

However, most DMs would also follow part of the rules for Raise Dead here. Body parts important for basic functioning aren't replaced by this item. It doesn't have the wording for that like a ring of regeneration does. If the creature removes your head from your body, this isn't going to fix that. I'm talking about the requirement that body parts essential for the creature to function, such as heads, being available and still attached.

As mentioned earlier, this paired with Dwarven Fortitude and Durable lets you heal a LOT on a Dodge (30 HP with 20 Con); doubly so on a character with relevant resistances, damage reduction and/or can Dodge with a bonus action.

I've got a hill dwarf rune knight fighter with Heavy Armor Master and the above feats. He regularly tanks with Dodge. If our party bumps into one of these, I'll definitely try to get it!

Warlock - celestial patron - pact of the chain with gift of the ever loving one's invication 

Thats double maxed*within 100ft of summon* heals up to 60hp garunteed as a bonus action (can only roll max of 5 consecutively)

Kinndddaaa juicy I'd say 

This is really powerful combined with Rage Beyond Death from Zealot Barbarian

It doesn't stabilize you until the start of your turn, so you die if you get hit three times in one round.

great for pets and sidekicks

Perfect for a Zealot barbarian.

Pretty useful item but I agree once you get higher lvls you shouldn't be dropping as much. If you think about it, its really the cost of a single Action since it equates to one of your party members walking over to you and using a healing kit (5 gold for 10 uses) and wasting their Action doing so.

That being said, certainly helps if your DM likes to attack you while you're down and also has the rule of Death Saves carry over until you finish a long rest.

This + wither and bloom = Profit.

Note that stabilizing is not the same as regaining consciousness, so if no one's healing you and you take 3 hits before your next turn, you'll die.

Ah lovely, removing all death saving throws with an uncommon item lol

Why is that so powerful.

Do you just heal everything? That is stupidly overpowered.

That people find this item overpowered is nothing short of amazing. Its good but takes up an attunement slot and is only useful if you fall. Won't save you from instant death or anything. Is it strong, sure. Overpowered? Hardly.

BryndenBlackfire, this has no benefit on Healing Light from the Celestial Warlock, this magic item only works when you regain Hit Points using your Hit Dice, which is usually only during short rests. It is not all healing.