Underdog - 15G (Requires Title Update 48)
Difficulty: Easy
Estimated Period of Time: Short
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To get this Achievement use 2 Controllers by signing your second controller in as a Guest, or else you'll have to get lucky against actual players.
While using a 2nd Controller, as soon as the match starts, purposely drop down to the lowest level just above the lava as your Main Account. Then as your 2nd Controller, throw yourself straight into the lava to get this Achievement.
(Unknown if you HAVE to play this in a Public Match, I personally did a Public Match to be safe and it worked, just make sure you and your 2nd Controller press the X button right away before annoying players join you. Would appreciate confirmation on the Public part)
(Also at the time I'm writing this Achievements are NOT being synced with the site yet, so don't panic if it isn't showing yet)
EDIT: "Worked in a private match! +1" - Alahert
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!