Time: 2013/12/21 12:19am (JST)
Frequency: 1
World name: Tonberry
Character name: Musou Tennin
NPC name: -
Monster name: Good King Moggle Mog XII
Class/Level: Black Mage Lv50
Party or solo: Party
In-game time: 2013/12/21 12:19am (JST)
Area and coordinates: Good King Moggle Mog XII encounter
Steps:
1. Killed most moogles (left 1 or 2).
2. All moogles should gather in the middle to summon Good King Moggle Mog XII.
3. One of the moogles is "permanently" dead.
4. The encounter freezes as Good King Moggle Mog XII won't spawn.
5. Party disbanded

Screenshots:

One of the moogles is still dead:


The dead moogle (so cute):