It's an egg where cute pet Christmas Snow Rabbit has fallen asleep in. With a portable incubator, you can wake up a sleeping monster.
Increases EXP by 5% (only during events in official servers).

[iRO Description]
An egg in which a cute Christmas Snow Rabbit pet rests. This can be hatched using a Pet Incubator.
Class: Pet
Diet: Candy
The following effects are active during the month of December.
Summoned Bonus
Matk + 2%
Increases the experience given from monsters by 2%.