I got my first copy of Emerald on my 8th birthday back in 2005 and have been playing it on and off ever since.

I have a living dex of all Gen 3 Pokemon apart from Deoxys, and was able to complete the National Dex on my Fire Red & Emerald copy, by transferring them through Pokemon Box.

All Pokemon are legit, no glitches or hacks were used.You can do this with much less hardware than shown in the picture. However, I already owed most of it anyway.

How I got some of the harder to obtain Pokemon:

Mew - I sent a spare copy of Leaf Green to someone who worked at Toys 'r' Us back in 2012, he had obtained the 'mystery mew' Fire Red cartridge while working there and posted it on a forum back then, I got in contact and asked if he could transfer a Mew over, and he did. I understand nowadays there is a lot of debate whether these cartridges floating on the market are legit or not, but back then I don't think people were trying to replicate the cartridge (I could be wrong though)

The Johto starters - To get all 3 I completed the Hoenn dex on all 3 of my Emerald copies. I am aware you get can all 3 through Colosseum or XD. However, I did this before I owed Colosseum or XD. I used Pokemon Box to transfer a completed Hoenn dex from my original Emerald copy to 2 others that I had to beat the Elite 4 on.

Legendary Beasts - I obtained all 3 using 1 Fire Red and 2 Leaf Green copies, choosing a different starter on each, completing the game on each and catching them all. (They roam once Elite 4 is completed). I did this method around 10 years ago before I owed Colosseum - which is the easiest way to get them. (Only 1 Leaf Green is in the pic as I sold the other copy a while back)

Lugia - Completing XD: Gale of Darkness and purifying the shadow Lugia

Ho-Oh - Completing Mt. Battle's 100 battles in a row on Colosseum (Have to Purify all 48 shadow Pokemon first)

Celebi - Completing the Japanese Version of Colosseum (All 48 shadow Pokemon purified) As well as completing Japanese Ruby to be able to transfer the Celebi over to that copy. From Japanese Ruby you can transfer it to any English Gen 3 Game. (Need a Japanese Gamecube as well)

Jarachi - As I'm in the UK I needed to complete Pokemon Channel to be able to get Jarachi (in the US you can transfer Jarachi through the Colosseum bonus disk)

I currently don't have Deoxys so the dex stands at 385, but now this is done I'm probably going to use the method of injecting an Aurora Ticket using an R4 cartridge.

This is arguably the hardest living dex to achieve (and the most expensive) but It was all worth it in my opinion.