The legendary team is made up of all the legendarys in all gameboy games

mewtwo-ceruleon cave,fire red\leaf green
mew-on faraway island,emerald
deoxys-birth island,all games
entie\suicune\raikou-depending on starter,fire red\leaf green
jirachi-nintendo event, emerald
ho-oh\lugia-navel rock island,emerald
raquaza-sky pillar,pokemon emerald
groudon\kyogre-marine cave\terra cave,emerald
articuno-seafoam islands,fire red\leaf green
zapdos-power plant,fire red\leaf green
moltres-MT.ember,fire red\leaf green
latios\latias-choose color on tv\southern island,emerald\ruby

If you capture these pokemon and put the strongest ones in your party your team will be impossible to beat unless someone does the same.