how do you catch regigas and deoxys?

to get deoxys you need to migrate him or use a AR and hack him.

ro get regigigas you need to get regice, regirock, registeel and press a at his satue at snow temple. first you need to solve a puzzle.

regice/regirock/registeel: you need to migrate for ruby/shapphire/emerald

deoxys you have to migrate or use AR.

for regigas you need registeel regiice and regirock(migrate from sapphire, ruby or emerald) go to the snow point temple and head to the bottom floor. Use ultra balls might take a while

or an easy way is to trade