Chaos Wrap

The owner of target permanent shuffles it into their library. Then they may look at the top card of their library and may wrap it. If it's a permanent card, they may put it onto the battlefield. Otherwise, they may put it onto the battlefield face down as a 4/4 red Present creature. (To wrap a card, put it inside lots of sleeves. If it would be dealt damage or destroyed, remove a sleeve from it instead.)

Nice

Search your library for a card and put it into another target player's hand. Then shuffle your library.

Naughty

Search another target player's library for a card and put that card into your hand. Then shuffle that player's library.

Naughty // Nice

Evil Presents

Put a creature card from your hand into play under target opponent's control. That creature attacks each turn if able . . . and always attacks its controller.

Present Arms

Exchange your library with another deck you own from outside the game. Shuffle your library.

Decorated Knight

Whenever Decorated Knight attacks, draw a card from your original deck if it's outside the game.

Decorated Knight // Present Arms

Topdeck the Halls

Decorated cards in your hand have miracle {S}. (Decorated cards include premiums, promos, and cards with alternate frames or art.)
At the beginning of your upkeep, if you control twelve or more decorated permanents, you win the game.

Fruitcake Elemental

Fruitcake Elemental is indestructible.
At the end of your turn, Fruitcake Elemental deals 7 damage to you.
{3}: Target player gains control of Fruitcake Elemental.

Last-Minute Chopping

Ask target opponent if they remembered to get you a present. If they say yes, they put a card they own from outside the game into your hand. Otherwise, you gain control of target permanent they control.

Bog Humbugs

Flying
Whenever Bog Humbugs deals combat damage, hum that many notes of a festive song. If you can, put a +1/+1 counter on Bog Humbugs.

Jegantha, the Wellspring

Companion — No card in your starting deck has more than one of the same mana symbol in its mana cost. (If this card is your chosen companion, you may put it into your hand from outside the game for {3} as a sorcery.)
{T}: Add {W}{U}{B}{R}{G}. This mana can't be spent to pay generic mana costs.

Thopter Pie Network

At the beginning of your upkeep, if you're eating, create a 1/1 colorless Thopter artifact creature token with flying. Use food to represent the token.
Whenever a creature token you control dies, if it's represented by food, eat it.

Snow Mercy

Whenever a creature deals damage to you, put a globe counter on it.
{T}, {Q}, {T}, {Q}, {T}: Tap all creatures with globe counters on them.

Yule Ooze

At the beginning of your upkeep, destroy another nonland permanent chosen at random, then put a number of +1/+1 counters on Yule Ooze equal to that permanent's converted mana cost.
{R}{G}, Eat some food: Regenerate Yule Ooze.

Season's Beatings

Family gathering — Each creature target player controls deals damage equal to its power to another random creature that player controls.

Some Disassembly Required

{B}, Sacrifice a creature: Distribute the sacrificed creature's keyword abilities among any number of other target creatures until end of turn. If it's December, you gain 1 life for each of those keywords.

Eggnogger's 'Stache

Lands you control have "{T}: Refill your mug with a festive drink." (If you don't have a mug, go grab a mug! It's the holidays!)
At the beginning of combat on your turn, if you have a drink 'stache, put two +1/+1 counters on each creature you control.

Goblin Sleigh Ride

Target creature you control climbs into Goblin Sleigh Ride. You slide them on their merry way. If the creature stayed on, it deals damage equal to its toughness to each other creature touched during the slide.

Gifts Given

Search target opponent's library for four cards with different names and reveal them. That player chooses two of those cards. Put the chosen cards into the player's graveyard and the rest into your hand. Then that player shuffles their library.

Kenrith, the Returned King

{R}: All creatures gain trample and haste until end of turn.
{1}{G}: Put a +1/+1 counter on target creature.
{2}{W}: Target player gains 5 life.
{3}{U}: Target player draws a card.
{4}{B}: Put target creature card from a graveyard onto the battlefield under its owner's control.

Mishra's Toy Workshop

{T}: Add {C}{C}{C}. Spend this mana only on spells and abilities that put tokens onto the battlefield. Use toys to represent the tokens.

Seasonal Sequels

Pitch the titles of up to X holiday-themed sequels to target spell. Copy that spell for each title pitched, except the copy has that name. You may choose new targets for the copies. (Simply adding numbers isn't festive enough.)