Click to go through professor Oak's text. Press space to encounter pokemon. Shiny chances: Without shiny charm: 1/400 With shiny charm: 1/200 Shiny armored mewtwo without shiny charm: 1/20,000 Shiny armored mewtwo with shiny charm: 1/10,000 1/50 chance of finding armored mewtwo.
Find 3 shinies and talk to professor Oak, he'll give you the shiny charm!