Super Tennis Blast (EP)

Very simple to obtain:

In Main Menu select MINIGAMES - BLOCKS - LEGEND and get at least 50 points.

So as the previous solution has stated, the achievement description is a bit misleading.
Putting the AI difficulty to Ultra Hard does not make the training harder or increase the "difficulty".

Your character has to reach a certain average skill level.
As your character's average skill level increases, so will the difficulty of the training.
You'll know the difficulty increased when you go to the week of your game and the Train button will have the word "Boost" underneath it.

For me, my character was at an average skill level of 87.
After I attempted power training, the achievement unlocked and it looked exactly like the video shown in the other solution.

I discuss how to obtain this achievement at about minute mark 4:30 in my walkthrough guide here:
The description seems to be a bit misleading.