Nethermancers

Nethermancers would be a really rare mob that spawns in the Nether, typically in Nether Wastes and even more rarely in Soulsand Valleys. They have the appearance of ancient Piglins in tattered red robes, having left their Bastions long ago to wander through the Nether to learn magic, necromancy in particular.

Nethermancers have three spells, the ability to cause the ground to erupt in flames, similarly to Wraiths in Minecraft Dungeons, zombify nearby Piglins and direct them to attack opponents, and a powerful (but rarely used) shockwave spell, to push back any foe that gets too close. Because of their dangerous magic, Piglins flee from Nethermancers and Piglin Brutes are actively hostile to them. Nethermancers are also hostile to Wither Skeletons and vice versa.

Being something of a mini-boss, Nethermancers could have around 80 health and, upon death, drop large amounts of gold ingots, experience and 1-3 of a new brewing ingredient which could be used to craft a potion that renders Piglins, Hoglins and villagers immune to zombification. (The drawback here is that if an immune villager is attacked by a zombie, they'll die without the safeguard of becoming curable zombies.)

This would make the Nether more dangerous and provide a fun, but rare encounter for players to either face or run away from. Plus, it adds to the story of the Nether.