How Do I Catch Deoxys Without Cheating Or Downloading In Pokemon Emerald?

You need to have 3 Pokemon level 100 and the national dex . Go to battle tower and beat it 3 times and then go to rowan and he gives you deoxys,Selebi,darkrai and when you go out side there is a explosion that is arceys he is there save before you catch him because he only stays for 1min

I hope that helped
and I like ronaldo.

I know an easier way beat the elite four 19 times talk to a lady on route 119 then go to mt.pyre talk to the old lady or man they will ask you for the magma emblem and one of your pokemon(I would prefer a weak one) then they will give you the Aurora ticket

Well actually, to catch deoxys in pokemon emerald you need to get mystery gift(I don't know how to do it) and  get new born island off of it and deoxys will appear. You may also get ho-oh and lugia too with mystery gift.

Most of the answers up top are right. You get the Aurora ticket at a nintendo event (Which are no longer available in the U.S.) then get it through mystery gift. When you go to the lilycove harbor and talk to the lady, she will get a sailor to talk to you and then they will take you to Birth island. Touch the triangle until it turns red in a time limit, and WAMMO! Deoxys will appear on level 30.    Hopes this helps!

As bi;Hy's Wei;Egegik

Rowan is the professor from pokemon Diamond pearl platinum

One answer I don't know either

Get the aurora ticket and go to 'Birth Island'.

Don't LISTEN TO ANY OF THE FAR OUT CRUD FROM ANYONE HERE. You either use gameshark, action replay, or p.c. Cheats. Or, you get an aurora ticket from a nintendo event( very tricky. You can check pokemon.com for info on the whereabouts.). Oh, and Rowan is the pokemon proffesor from diamond, pearl, and platinum.

Go to the pokemon league run in the wild for a long time you will find him there

You get the aurora ticket via special event and then fly to mosdeep and talk to the old man in the space center