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Not only did roamers disappear when they roared, but roamers in RS and FRLG were guaranteed to have horrific IVs because of a data transfer glitch. They had normal HP IV, attack capped at 8, and everything else would always be zero.
Maybe they simply used a bigger cart. Just like they don't have to use anthing bigger than a 256MB card for BW1, they probably used a smaller storage device for Red/Green.
in black and white, if u look closely at klinklang once u choose a move, the sprite will stop for a second. its funny cuz klinklangs pokedex description says its dangerous if it stops spinning. so i lol'ed at that.