The event starts December 27th and goes until January 7th. There are two halves to the event.
In the first half (starting on December 27th):
types of seasonal seeds are available for planting: white peony seeds
and purple peony seeds. Both types of seeds can be received by
animal requests. White peony seeds can be purchased from Lloid. Purple peony seeds can be received by sharing plum ripplewings and citrus ripplewings in other people's gardens.
Two types of rare
creatures can be acquired. Plum ripplewings can be found on newly
bloomed white peonies. Citrus ripplewings can be found on newly bloomed purple peonies.
In the second half (starting on December 31st):
new type of seed is available: red peony seeds. They can be acquired
from completing requests or sharing blossom ripplewings or ornamental ripplewings in other's gardens.
Two types of ripplewings, blossom and ornamental, can be found on newly bloomed red peonies.
Capture enough of each type to gain prizes ranging from snowballs and Leaf Tickets to clothing and furniture.
This event in particular contains "Hard Tasks". These are bonus tasks for
the event once you have completed the regular ones needed to acquire
all the items. Completing hard tasks will grant you recoloured versions
of items obtained throughout the event. Note that these items will not
appear in the catalog, and will not count towards event completion.
See more information on Chilly Jamboree events here.