The Everfight Staff is a staff.
When used, the player will gain the resistance effect. The duration of the resistance effect depends on how much health the player is currently missing. E.G. 15 seconds of resistance at 75% HP, 30 seconds of resistance at 50% HP, with the duration going up to 60 seconds. Everfight Staff will not work if the player is at full health.
Everfight Staff is currently unobtainable in survival mode. It can still be spawned in via Creative mode, commands, or other third-party methods though.