Sacred 3

If you want to legitimately you can unfold the spoiler. Otherwise find a friend on an Xbox One with a level 50 character who can help you out by quitting as you join in.

Here is how that goes:
Xbox One person takes a level 50 character and will now be named Emulator
The person going for the level up will be called the Receiver

The Emulator invites the Receiver after the Receiver has at least completed or quitted out of Halios when selected a (new) character.
The Emulator then launches any mission immediatly. (I recommend Asgarth)
The Receiver will join / accept the invite when the Emulator is in the cutscene
As soon as the Emulator then sees: "Player is joining the Enemies are growing stronger" he will skip the cutscene, drop his character into the mission and immediatly quit the emulation by pressing the guide button, then and quit the game.

Explanation
Since there is a delay in joining, you should be about a loading screen behind. So when the emulator is quitting, the receiver is still in loading screen where a shield like icon is filling up. After that there should be a host migration and the level stats will be transfered. Because the host quit, your mission will restart as normal but you are now level 50. The receiver then quits out and you will see obtaining tons of xp all the way to level 50. You will then earn this achievement

The solo grind recipy: