When Witch Hunt deals 4 damage to a player who isn't the owner and dies as a result, what happens to the Witch Hunt enchantment? Does it get exiled when the player dies or returns under its owner's control?

I've come across this rule recently but if I control Prossh, Skyraider of Kher *f-etch* and have created 6 Kobolds of Kher Keep with Blood Artist on the field, if another player casts Leyline of the Void, if I sacrificed my tokens after Leyline of the Void has resolved, I would still get the Blood Artist triggers because they're not cards?

I ask the question what happens when I cast an Ixidron and follow it up by casting a Detention Sphere on a face-down creature? From what I understand, they don't have names so Detention Sphere wouldn't exile each player's board excluding the Ixidron. Is my assumption correct?

If I cast Tax Collector and elect the mode to make my opponent's spells cost an additional generic mana, if I then cast a Opt and my opponent responds with a Force of Will, would they have to pay the additional ? What's the difference between this effect and Trinisphere?