Snowplough - 15G (Requires Title Update 48)
Difficulty: Easy
Estimated Period of Time: Short
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To get this Achievement use 4 Controllers by signing your second, third, and fourth controllers in as Guests, or else you'll have to get lucky against actual players.
While using multiple controllers, as soon as the match starts, purposely drop all four controllers to the last level above the lava. Then position your 2nd, 3rd, and 4th controllers on the edge and pelt them with Snowballs from your Main Account to knock them into the lava and get this Achievement.
EDIT: "This achievement is cumulative, meaning that you only need 1 other controller or person and you can knock the same opponent into the lava in 3 different rounds. Also it does not need to be an Online or Public game." - Dyssident
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!