Legend Ribbon is something earned by defeating Red in HGSS, cool, so that is actually valid. Didn't know about it, being DPPt mod. :P
IVs are 18 / 8 / 21 / 11 / 3 / 29, which do appear to be legal when tested on Smogon's IV to PID
applet.
EVs are just 2 in special defense, so someone probably beat a Tentacool and used Rare Candy afterwards.
Level 50 from Newmoon is fine.
ID and number are not blacklisted on my sources.
Basic verdict is that Darkrai is legal and you can trade it. :q