what does it mean to have a themed pet like what even is it?

A themed pet is one that can only be created (or caught) during a special event of some kind, like, for example, the Heavenly Ferikki & three different Puffadores we can get right now.

Other Examples
Winter Tanuki Lupora


Yuletide Tree Nytekrie


Black Ice Zolnixi

All three of these were only creatable/catchable during this past years Winter Festival.


Black Widow Sylvorpa


Dusky Dawn Zolnixi

Both of these were only creatable/catchable during the Fall Festival this past year.


Beach Day Sylvorpa

This one could only be created/caught during the past years Summer Festival.


While themed pets are attainable after the event in which they were originally introduced ends, they tend to be very expensive (20k gold and higher), because of their exclusive nature.

Basically, Themes are official site colour sets for pets- all pets of the same theme share the same colour set (with slight colour fluctuation within a strict limitation)

There are two kinds of Themed pets- Tamed ("Zone") and Exclusive (with some subsets of Exclusive).

Tamed Themes can only be obtained from Festival Zones (with the exception of the Lost Grove themes, which can only be found in the Lost Grove)
Each Festival gets its own set of themes, and they rotate out on a cycle.

for example, Moonlight Luffox


Were available to catch in Winter Fest 2014 and 2015m and then retired permanently.

(also there is never a Zone themed of: Puffadore, Ny'vene, Seasonal fableds of the other seasons (only the current season))


Exclusive pets can be obtained in several ways, depending on what the theme is.
For example, currentlyyou can buy (until the end of today) or potentially create (via Candy Combining) a Heavenly Ferrikki, and you can buy the Cupid's Angelic Puffadore Egg, which contains one of three puff themes (in previous years, there were bosses you could run into that could drop an eggling)

During Fests, there are the Battle/Nurture boards (generally three rounds per fest), where the top places get an eggling of the species they were fighting to get points for. These boards have a new theme every year (in every fest)

There is also pet Creation via activities like Sand Sylesti Building (summer) of Brewing (Fall) which can make either the new (the same as those obtainable via the battle/nurture Boards) or the ones that were new the previous year


Winter Snow Griffi, obtainable via boards or creating in Winter 2017/18 and via creating only in Winter 2018/19

Other subsets, usually more expensive:
Majestic Themes (themes with Restricted traits, see Restricted/Majestic guide in player guides forum)
Wheel themes (original Wheel is now permanently retired. These guys are the Exclusiviest Exclusives.)

There's a (currently not completed, but comprehensive in all that is there) guide to themes here