Mew: hacked. Shiny Mew can only be from a Japanese Emerald game; this Mew has its English name
Darkrai #1: almost definitely hacked. From the image, that looks like a Dream Ball, which I am 98% sure is illegal on Darkrai
Darkrai #2: probably hacked? The fact that it’s “Darkrai” and not “DARKRAI” suggests that it originated in Gen 5, in which case, it’s definitely hacked; all Darkrai events in Gen 5 were shiny locked. If it says that it originated from Sinnoh, then it’s possible that someone shiny hunted for it in Gen 4 and then manually lowercased its name before transferring it.
Darkrai #3: possible. The caps-locked name suggests that it originated from Gen 4, where it’s possible to catch it in a Master Ball.
Shaymin: hacked. Friend Ball Shaymin is illegal.
Arceus #1: possible. The name suggests Gen 5, and it’s possible to catch Arceus in a Premier Ball in the Entree Forest.
Arceus #2: hacked. The hacker wanted to make it look like it was from the Azure Flute event, where it would theoretically be shiny huntable, but that event was never officially distributed. The first (and only) time shiny Arceus has been legally obtainable was in Gen 6.
Metagross: technically possible, but almost definitely hacked. Running its stats through a calculator show it to have perfect 6IVs (and fully EV trained) with a perfect nature, too. Getting a 6IV Pokémon in a Gen 5 game, in the absolute best-case scenario, is less than 1 in 32,000. Then put shininess and the nature on top of it.
Magmortar: technically possible, but almost definitely hacked. Exact same situation as Metagross.
Celebi: hacked. Any shiny Celebi is hacked except for those hunted in the VC of Crystal, which can only be transferred to Gen 7.