it only affects who goes first (unless use of quick attack or extremespeed), but i dunno what will happen if two monsters of same speed attacks, random? the fastest pokemon is electrode, followed by mewtwo but what i found really odd is that aerodactyl is really fast, even if it is a rock type! slaking is faster than my gyarados and vigoroth! (how?) the slowest ones are shuckle and torkoal (dammit, how long will it take?) equip some monsters with quick claw and they might probably go first... also, i found out they lower the enemy trainer's pokemon stats a lot because how else would my feraligatr be faster than red's pikachu and charizard?! i really dont know how they calculate it, but speed definetely shows who goes first! (electric and psychics are the fastest, sometimes!)