LF one last pokemon to complete my dex! (I put the name in the title last time without realising that doesn't fly here)

[r]

Palkia is the LAST pokemon I need to complete my dex! I just need to own it once, so I'll trade collateral for peace of mind :)

Also, I tried to trade my Darkrai for it on GTS but it said I can't because it's a special pokemon, what does that mean?