Fogbound Lake is one of the three lakes that have a Time Gear. The lake is guarded by Uxie, one of the 3 lake guardians. During their first encounter, the player and his or her partner will battle a Groudon, however, this Groudon is just a mere illusion Uxie can create, thus, you cannot recruit the Groudon illusion. After you defeat the fake Groudon, Uxie will appear and lead you to Fogbound Lake, where there is Volbeat and Illumise flying around the lake. Wigglytuff will suddenly appear and say friend to Uxie and the fake Groudon. The rest of the guild will appear and jump in fear as they see the Groudon illusion. After Uxie explains more of Fogbound Lake,the guild goes back to their place. But, before that, the Guild makes a promise with Uxie not to tell anyone about Fogbound Lake or he'll erase their memory.
After the main story, if you go up to Fogbound Lake, which is labeled, Steam Cave, you will battle Uxie, if you succeed, you can recruit Uxie.