If someone has sniped you, then you should be their acquaintance and therefore have access to their IGN (and depending on what they traded you), their ID Number. If these can be linked to a particular user, then you could message a mod and there's probably a reasonable chance that you could get them banned.
Do you have the capacity to clone? Because truth be told I'd quite like a copy of your Landorus-T (the one without the Nickname) if possible.
If you need me to I can clone it - a copy for you, a copy for me and a copy for Theory