This can easily be achieved in a matter of minutes. Here's step by step instructions for how to unlock this easily. From the main menu select Local > Versus Mode. Hover over the second player spot and press
to assign it to another human player. This can be done with only one controller! For P1, select Wrastor as your character. P2 can be any character. Press
to go to the stage select screen. From there, select the stage "The Rock Wall". I chose this stage because there is less chance of the second player accidentally falling off the sides of the main platform.
Once in the stage, go below the second character and HOLD
to do Wrastor's neutral special move. Don't just press
because you won't get enough height. Wrastor should spin in a tornado and move upwards almost to the top of the screen. Fortunately, you're able to control the direction of the character a little while you move. Try to keep your opponent between the two pillars because the pillars will eventually break after receiving too much damage, and you could accidentally get the KO at the bottom of the screen when it needs to be the top of the screen for the achievement.
Keep spamming this attack to damage your opponent, and once their damage has reached about 150%, they will be eliminated at the top of the screen and this high-ratio achievement will be all yours!