I saw a shiny Watchog and it required like a Serperior (I picked Tepig). All the Serperiors required like a lv. 9 and under Zekrom. I was pretty pissed.
But I did trade for an Accelgor, which was awesome, since I wasn't able to trade with myself or a friend at that point.
Overall GTS sucks though. I heard your Pokemon may disappear after awhile, so that scared me.