I've seen a lot of posts about why Witch XP farms are impractical. I've got a Witch Farm where I get good XP and, more importantly, lots of rare potion drops.
I used docm77's witch farm, and added my own touches. Instead of an instant drop, I collect the witches in a mob kill box. The witches stand on a sticky piston connected to a block over a 40 block high drop.
The secret to making this work is that any mob that dies withing 5 seconds of getting hit by the player is considered a player kill. So, I collect a bunch of witches and throw in a splash potion of harming. Witches have 80% immunity to harming potions, so the splash potion will only give them each a tiny bit of damage, but the game still registers that I have hit them.Then, I quickly press a button to drop them down the chute.
The Witches die from the fall, but since they die within 5 seconds of getting hit by me, I get all the XP for their deaths. (The fall itself takes 2-3 seconds, so I have to be quick about hitting the drop button.) Additionally, since they all took some damage from the splash potion, they will often pull out their own potion during the fall. They will have the potion in their hands when they die, and since I technically killed them, they can drop the potions as rare drops. They usually pull out swiftness or healing potions. But I also found a way to farm Fire Resistance Potions.
After 10 blocks, mobs will fall through a single liquid block without stopping or swimming. So, at 10 blocks below the kill box, I have the tip of a lava blade (the fourth block from a lava source). The witches fall through the small lava block and catch fire. Because they are on fire, many of them will pull out a Fire Resistance Potion before they hit the ground and die. After a few dozen kills I easily have a double chest full of fire resistance potions.
It's not the most efficient XP farm, since you have to go down to the bottom of the chute to collect the XP. But the method makes Fire Resistance Potions available BEFORE you go to the Nether for the first time.
If I get a chance to record a YouTube video, I will put up a short demo of how it works.
Look at all that cheddar! Notice the 2 fire resistance potions. There is also a swiftness potion in there.
Mobs in the collection kill box. They are standing on a block connected to a sticky piston. The button will cause the piston to retract.
View of the tip of the lava blade, seen from above.
Well I would like to point out, well this is a well thought out design, the purpose for me having a witch farm is so I can get the loot without having to kill them myself and be able to leave my game afk or go run around and do other things and come back to some redstone and glowstone.
I can think of something that may help you though. Instead of throwing your splash potion and then quickly pressing the button to drop them, you can set up some tripwire hooks connecting to the sticky piston drop mechanism. The splash potion should trigger the tripwire and drop them. You may or may not need a repeater to delay the piston for a second so potion has time to hit the witches before the fall
magboneD, I salute you. I've been trying to think of ways to get the witches to drop their potions in semi-automated way, to farm it essentially, and I couldn't think of anything better then collecting them in a chamber, and then using a crusher and a good sword to kill them for healing potions, pouring lava on them briefly and then good sword for fire resistance and throwing a potion of slowness at them to get them to drink a potion of swiftness, and using a good sword, once again.
suffice to say, your method is MUCH more efficient and clever; I like joonatan1998 and crumpetxxix's ideas too, further automating and streamlining the operation of gathering and using witch drops! would throwing the potion really trigger the tripwire crumpet? I had no idea, I need to experiment in creative more.
witches will also drink potions of water breathing as well from 1.7 onwards I believe, which means you can add a dispenser system that briefly drowns them before dropping them too, for the chance to get those potions! and you could install a water drop to get down to get the XP quickly, and a water/sign elevator and/or an ender pearl elevator - tripwires closing the floor when you enderpearl into the ceiling - or simply a minecart railway spiralling up and down to get up and down between the drop kill at the bottom and the collection chamber at the top before the drop quickly. actually... would a water stream funnel the xp around? because you could get a water stream to funnel the xp orbs back up to you, right?
so many possibilities! but the basic principle that hitting a mob means it's counted as your kill if they die within 5 seconds, and the elegant way you've exploited that to get the witches' rare drop potions, is ingenious, and i'm amazed no one's thought of this before - and if anyone has, then I certainly haven't seen it anywhere else. kudos, magboneD! I'm going to try this in my world when I build my witch farm!
Aw no I just tested it, it doesn't trip the wire. That sucks. Pretty much any other entity does including just throwing an item so I assumed it would.