STEVE's Second Chance

Sleeping sets up the mod's protection. The first time the player would die afterward, the death is prevented, in a way similar to a Totem of Undying. Activating the Second Chance before a later fatal hit is what triggers the effect, and it does not stop death for the player once the protection has been used.

When the effect fires, the player is healed to half of maximum health and receives a short burst of Speed for 2.5 seconds to help them escape. Beeps sound for 30 seconds, and at the end the player is left with very little health. A later use of the mechanic is handled as a third chance, which the author text describes as a separate case.

The mod is a Forge mod for 1.12.2, published as version 1.1 and released under the MIT License. It is not open source. The server and every player need the mod installed.