Showdowns kinda fun you can choose what EV/IV's your pokemon have. Its just pure battling, but becasue you can have any pokemon it kinda takes away the achievement you get from building your team from scratch like you would in the normal game.
I have not wonder traded in well over a year, mostly as I read you can get wondertraded a "bad egg" which corrupts your game, that may be a load of rubbish though. Also like you I am suspicious of Hacked pokemon out there.
Yeah that Gallade seems very suspicious, the chances of hatching a perfect IV shiny most be slim to near impossable.