Mewtwo, or Articuno. I used my Masterball on an Arbok, even though I was completely capable of reading and quite smart, I thought the game must of been kidding, saying I could catch any Pokemon without fail. Never encountered Raikou/Suicune or Entei. Chansey and Scyther were just crap. Looked for hours and finally found 3 Scyther. but only caught one. Oh yeah, I was 6 when I got it.