grey area. in us if you own the game and you rip the rom from the game your self it's perfectly legal to have roms,HOWEVER in places like europe,even if you own the legit game it's still illegal. also unless you live in china,downloading roms is illegal regardless of any ownership.
but it's not like the feds are gonna bust your door down,just refrain from speaking of it on gamefaqs.
Jirachi is the best pokemon Please check out my pokemon lp:http://www.youtube.com/watch?v=ty0G7lOSuaU
You would never be sued for this. There is just no way to know, neither a company would give themselves the trouble of one legal action, since they would need to prossecute a good part, and this is absurdly inviable.
It is all up to your moral and good will. There is nothing more than this. It is illegal? Yes, because it is using intelectual property without its owner's consent. Considering that Nintendo is a Japanese comapny that is present in many countries, it obviously violates more than one juridical order in some sense.
What will happen if you play it? Nothing. That is the truth. It is beyond me why are you asking, though. It is up to you, having in mind that yours action added with thousands of others can hurt Nintendo and therefore, Pokemon in certain ways. It is recommended to not do it, but if you do, nothing is stopping you.
Proud designer of Chip, the Runner Up Megaman Legends 3's Mascot Contest! http://tinyurl.com/3r6wb4u