Speak to Isaac in Frostfort @ 488 51 163
Interview the locals to find Uxie's hiding spot.
Find Hielo @ 385 53 166
Find Barafa @ 432 74 150
Find Muz @ 370 88 135
Go back and speak to Isaac @ 488 51 163
Find the hidden cave entrance @ 341 88 104
Go into the cave and defeat the Cosmic Star Grunts.
First Grunt @ 321 83 141
Battle:
Level 20 Cloyster
Level 21 Snover
Second Grunt @ 289 60 79
Battle:
Level 21 Sneasel
Level 21 Snover
Third Grunt @ 267 44 58
Battle:
Level 22 Snover
Level 22 Jynx
Level 22 Delibird
Fourth Grunt @ 290 31 78
Battle:
Level 23 Miltank
Level 22 Golbat
Level 22 Sealeo
Warning: If you walk close enough to Danielle & Isaac, you are immediately forced into battle without having to speak to the general!
Cosmic Star General @ 304 30 76
Battle:
Level 25 Gallade
Level 24 Porygon-Z
Level 24 Skorupi
Level 25 Tangela
Once you have defeated the Cosmic Star General, you have completed the quest and will receive these rewards:
