>>20953740Pretty much this, GTS gets a bad rep because they don't filter out the impossible requests while fair requests disappear almost instantly. The result is a GTS that looks much worse then it is.
All you need is a couple legendary pokemon from any game that isn't gen 6, hell you might even get away with those too, but I never tried.
Once you've got something non-standard you can just keep trading through all the legendary lines. Put up the request for something you need and eventually some someone will come along doing the same. Round robin until you've got every non-event pokemon. The genies took me the longest, but even that was relatively quick.
This works with non-legendary pokemon too of course. I remember breeding tyrogues to trade on GTS for other gen exclusive mons, it's pretty quick most the time. The trick to GTS is putting up offers on your own terms, searching the GTS for fair trades is a pain in the ass, anything fair will be completed quickly.
