How to Catch the Mewtwo I Caught in Pokemon Black

I finished Chapter 3 in The Rise of ThornClan.
Here is a simple step by step guide on how to catch the Mewtwo I caught. You must have Pokemon Black and have beaten the first gym.
Note: This is probably a glitch so you might not get the same result.

1. Enter Wellspring Cave (Cave on Route 3). Make sure to save.
2. Walk alongside the right-hand wall until it bends.
3. Run into the wall on the spot right after the wall bends.
4. Run in to the wall 6 more times.
5. The wall should collapse and you should hear a glitched Mewtwo say "Mrooowow! Mroo!" If not, turn the power off and try again.
6. Walk past the crumbled wall into a hidden area that is actually a cave in Pokemon Red (I found this out later).
7. If you are lucky, there will be no more glitches (If so, turn off the power and try again). Approach the Mewtwo and it will challenge you.
8. Throw a Quick Ball at it or decrease its HP and catch it with a Dusk Ball.
9. If you catch it, save immediately(If you don't save, the Mewtwo will disappear after you leave the hidden area. I experimented with this).
10. Congratulations! You just caught a glitched, impossibly strong, and awesome Mewtwo!

Comment if this method works and any promblems with my guide.