Snag List :: Colosseum here

This is a list of the Shadow Pokémon you can snag in the game (in order).

Makuhita
Bayleef
Quilava
Croconaw
Slugma
Quagsire
Skiploom
Flaafy
Noctowl
Misdreavus
Furret
Yanma
Remoraid
Mantine
Quilfish
Meditite
Dunsparce
Swablu
Sudowoodo
Hitmontop
Entei
Ledian
Suicune
Gligar
Stantler
Piloswine
Sneasel
Aipom
Murkrow
Forretress
Ariados
Granbull
Vibrava
Raikou
Delibird
Sunflora
Heracross
Skarmory
Miltank
Absol
Houndoom
Tropius
Metagross
Tyranitar
Ursaring
Smeargle
Shuckle
Togetic

About Snagging Shadow Pokémon-
Snagging Shadow Pokémon is just like capturing them in the wild. When you see one, weaken it and simply throw a ball to hopefully catch it successfully. However, this is by far easily said than done- as you get further in the game, you will obviously meet much stronger shadow Pokémon that are much more difficult to catch than weaker ones. I have created a list below full of strategies that may help you snag 'em all.

Try your hardest never to kill a Shadow Pokémon, but make sure to lower its HP until there is nearly none left.
Use a variety of effect-techniques such as Hypnosis or Thunder Wave to make snagging easier.
Use better balls for stronger Pokémon. Example- if you are trying to snag a lv.47 Skarmory, use Ultra Balls to catch it.
Never use super-effective attacks on Shadow Pokémon you are trying to snag.
If you accidentally K.O. a Shadow Pokémon, don't freak out; you can always try to snag that same one again in a while - except for the Legendary Dogs, whom you only get two chances to snag.

About Shadow Pokémon-
Every Shadow Pokémon knows the attack, "Shadow Rush". This attack has no type, but it causes its user to take recoil damage after use. Using Shadow Rush can also cause a Shadow Pokémon to enter Hyper Mode, which raises the ratio of Critical Hits for that attack. When a Shadow Pokémon is in Hyper Mode, you can also call it- this helps reduce its shadow gauge until its empty.

Unfortunately, although Shadow Pokémon sounds cool to all of us, they do have bad disadvantages compared to normal Pokémon. First of all, they cannot learn any new attacks (by TMs). Second, they cannot be nicknamed or receive exp points after battles. However, donï¿½t start stressing yet- after Shadow Pokémon have been totally purified at the ancient shrine in the Relic Forest, they will gain all the exp points they have gained in previous battles (to learn more about purifying Shadow Pokémon, read my Pokémon Colosseum review).

Conclusion-
Overall, Shadow Pokémon are like regular Pokémon that need to be trained until their hearts open up to their trainers. Although it might take some time to do so, it's totally worth it in the end. I hope this guide has helped you, but all I can say now is - Happy snagging!