Taste of Your Own Medicine - 20G (Requires Title Update 48)
Difficulty: Medium
Estimated Period of Time: Varies
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To get this Achievement, load up the new Elytra Tutorial. Head into the village and turn right to find the Fireworks and Potions area at the coordinates: X: 4, Y: 79, Z: -41. Open the chest in the Potion area to get an Empty Bottle, Nether Wart, and Blaze Powder. Fill a Bottle with water from the nearby cauldron of water.
Next you'll have to do some hunting. Make sure you are on Easy or Harder and kill a Creeper without it exploding to get Gunpowder. Then find Spiders and kill them until you get a Spider Eye (NOT Fermented Spider Eyes) Once you have these, return to the Brewing Stand at the Potion area.
EDIT: You can get Gunpowder from the Fireworks chest next to the Potion area at: X: 0, Y: 79, Z: -32. Thanks to LuckyKacper2005 for the info.
EDIT: Sweet Rung has found a Spider Spawner at the coordinates: X: -60 Y: 70 Z: -93
Enter the Brewing Stand interface and put the Blaze Powder in the upper left corner slot as the heat source. Next put the Bottle of Water in the first of the 3 lower slots, then put the Nether Wart in the top slot. Wait until the arrow fills and the Bottle of Water will become an Awkward Potion. Next replace the Nether Wart spot with the Spider Eye and the Awkward Potion will become a Potion of Poison. Next replace the Spider Eye slot with Gunpowder to get a Splash Potion of Poison.
With this in hand simply find a Witch (looks like a green villager with a pointy hat) and throw the potion at her. It may take a while to find a witch but once she sees you she will throw poison potions at you to give herself away.
IMPORTANT NOTE: Thanks to LordFightALot a solution has been found for anyone that was trapped with relocked Achievements on the day of Title Update 48's release! Do as follows and there is a 99% of it working!
"This is exactly what I did:
1. Start up the Xbox (it auto signed in for me)
2. Manually sign out of your profile on the Xbox dashboard.
3. Launch Minecraft.
4. Press Play Game
5. A popup appears and asks you to sign in. Press Yes [I want to sign in].
6. The achievements popped right away on the world selection screen."
If this worked for you, don't thank me, go thank LordFightALot!