Money Money Money
A Kewl Tune deck will run you somewhere in the neighborhood of 600 dollars - but almost half of it is tied up in this handtrap.
Fydraulis Harmonia
This Fairy Tail monster is based on the Tale of the Bamboo Cutter.
Luna
Manticore of Darkness
FIRE
Cube
Number 85: Crazy Box
The 2011 Advent Calendar featured Blackwings and Junk cards, designed to gift children this extra deck type on Christmas day.
Synchro
Azamina Light and Darkness Ritual demands Yugiboomers invested well as a kid - mostly to afford this 60-dollar 3-of.
Black Chaos
An extremely-expensive card a few sets back, this electromagnet sees heavy play as a Naturia Beast enabler.
Beta
Elemental HERO Flame Wingman
WIND
Hope
Number 39: Utopia
The 2019 Advent Calendar eschewed the Christmas theming, and replaced it exclusively with cards featuring this monster and its retrains.
Kuriboh
Power Patron isn't too expensive - but you'll need to drop 7 or 8 bucks on this TCG-exclusive Pendulum monster.
Shade the Obscure
Each exosister has a promised sister named on their card - except for this exosister, who is named on two. She gets around!
Elis
Pyrite Knight
EARTH
Sun
Number 09: Dyson Sphere
A german exclusive, the 2014 Advent Calendar featured exclusively cards of this extra deck type (and GEPD and Santa Claws).
XYZ
Everything's a bit expensive now thanks to this recently-released hand sculpting tool - I'm just too lazy to grind.
Pot of Sloth
As part of an attempt to modernize Ritual summoning, Rush Duel just received this Mant, which finally lives in the extra deck
Zera
Flying Fortress - SKY FIRE
WIND
Spider
Number 35: Ravenous Tarantula
In-between Toy Magician and Ghost Reaper and Winter Cherries, the 2018 Advent Calendar pays homage to your uncle who got too drunk at the Christmas party with a reprint of this XYZ monster.
Number 41: Bagooska the Terribly Tired Tapir
Even though it's seeing no play whatsoever, rogue decks that can splash spellcasters are paying through the nose for this fusion monster.
Dark Magician of Destruction
The least-popular of the Aesir monsters, this never-used god can negate spell/traps during the battle phase.
Loki
Geira Guile the Cubic King
Ruler
Number 11: Big Eye
The 2018 Advent Calendar's Christmas theming culminated with this trap card, to be opened the night before Christmas.
Oh Tokenbaum!