Staff of Banishing

Proposal for a devastating one-time use (and ideally difficult-to-obtain) magical item. 

The Staff of Banishing would be a projectile weapon, usable only once on a full charge. It would likely be crafted from crying obsidian, a totem of undying, and a wither rose (subject to change for balancing rarity). To use the staff, the casting player would have to charge the staff for a few seconds as though they were drawing back a bow, meanwhile the caster's health would drop, reaching 0.5 health at its maximum charge.

When a player is struck by the staff's projectile, they are "banished" to the nether (teleported to a random unexplored part of the nether) and spawned there with a new block, the Cursed Respawn Anchor, which behaves like a regular Respawn Anchor block, except it has an unlimited charge until the player enters a nether portal, and it can't be broken in survival. The contents of their inventory would be dropped in the overworld where they were hit, as though they had died. This item would have its own unique message, as one would expect: "<Player A> was banished by <Player B>." A banished player has to either find or build a nether portal to escape the nether.

The staff's projectile would simply despawn mobs (not including Withers or Ender Dragons), and would explode when used in the nether, like beds. Whether or not the player's projectile lands, the staff will be consumed and their health will have been drained. After use, the player receives poison and slowness effects.