Skulk Scythe ~ a weapon that turns mobs into ghosts

Upon killing a mob using a skulk scythe, the mob will turn into a "ghost" or "soul" version of itself, which would look similar to how allays already look but translucent, or like the ethereal warden concept art. Importantly, you can only see ghost mobs whilst holding the scythe, otherwise they appear completely invisible. Making mobs permanently invisible would allow for new creative ideas, notably with the sulfur cube which shows the block inside of it when it's invisible. Other interactions that mobs have with leads, boats, etc. could be turned into interesting ideas with invisible mobs.

To permanently kill a ghost mob, simply kill it again with the skulk scythe. You cannot turn a ghost back into a living mob.

Hostile mobs could be given different behavior whilst in ghost mode, allowing a new combat experience. I propose that hostile mobs will only target players that can see them (holding the skulk scythe), and could be buffed or given new abilities to make them more challenging to kill, but also have loot (in theme with skulk/souls) that would encourage players to fight them.