An item that automatically revives someone once they have been Knocked Out.

Exactly what the title says.

An example of this would be the Life Shrooms from the first 3 Paper Mario games, or even the Revival from Dokapon Kingdom. If you're making an RPG with only 1
playable character, it is practically a necessity.

I've seen similar posts to this, but none have ever returned a conclusive solution.

I am also open to the use of plugins to make this a possibility. If you were to create a plugin based around this, It would most likely be as simple as; When a character dies in battle, the game checks for an item in the party inventory that has a notetag like <Auto Revive> or something like that. Then, a sound and animation would play, and the player would be revived. A formula could also be specified in the notetag as well.

So, any ideas?

I think if you make the item equip-able, you only need this:

http://yanfly.moe/2016/05/28/tips-tricks-auto-life-rpg-maker-mv/

Buff/State Core and State Categories
State Note Tag
<Category: Bypass Death Removal>
<Custom Deselect Effect>
if (target.hp <= 0 || target.isDead()) {
target.startAnimation(49);
var heal = Math.floor(target.mhp * 0.50);
target.removeState(stateId);
target.gainHp(heal);
target.startDamagePopup();
target.clearResult();
}
</Custom Deselect Effect>

from the sounds of it u just need someone who can add to this.
&& party.item id phoenix down
and party.gainItem -1 phoenix down

however that gets worded in these things

also taking out the remove state if someone can help and just using a <Passive State: x> so its a permanent thing as long as still have the item

mine is setup so use item/spell before you die to get the auto-life state which gets removed when you revive