HOW TO SET UP DNS WIFI:
1. Go into your 3DS's system settings (DS models can work with some extra meddling though a 3DS streamlines the process greatly)
2. Choose your primary internet setting and go to the DNS section.
3. Turn off the Auto-Obtain DNS setting
4. Enter 178.62.43.212 as your primary DNS (Leave the secondary DNS blank)
If you did this correctly, Gen 5 WiFi functionality should now be reenabled. Simply turn Auto-Obtain DNS back on to restore full internet functionality for your 3DS.
List of active and open Gen5 GTS Trades:
https://pkmnclassic.net/gts/List of obtainable Mystery Gift Pokemon, per game:
https://pastebin.com/ymLzRj5X 