How do you recruit golduck in explorers of sky?

well firstly the groudon in steam cave is FAKE!

the real groudon is when you complete the game and complete the dungeon "shimmar desert" at the end of the dungeon you fight groudon, defeat him and with a bit of luck you can recruit him.

you can onley unlock shimmar desert after you found sizor and obtaind secret rank.

then go to spinda café and talk to the Pokemon at the entrance there are seven of these dungeons.