Hearthpwn

The role Chair Millhouse plays in this expansion is similar to that of C'Thun in WOG. The card is given to players for free, and if you want to build a deck around it, you need several other cards that refer to Chair Millhouse by name.

The UI (user interface) when you play a card with Voodoo is like the Choose One cards UI. You pick one side and that's the effect you get. Some Voodoo add new effects and some replace the base effect (all ended in instead), you can see both examples under this lines (they're cards from Phase I). 

Remember: you can die if you don't have enough Health and you activate the Voodoo side of the card! 

The Void Orb mechanic allows you to use Void Orbs as payment for additional effects with some cards.

Cards like Deathcaller, Spirit of Fear and Follower of Zivius will give you Void Orbs when you play them, where you will store them until you use them. Void Orbs are store beneath your Mana Crystals just Overload, and you are capped at 10 Void Orbs.

Other cards like Twilight Embracer, Dragon Knight and Zivius are what will allow you to actually use these Void Orbs to your advantage. When you play a card like this, you can choose how many Orbs you spend. A Discover-like interface will pop up giving you options of numbers up to the number of Void Orbs you have (including 0 if you don't wish to spend any). The more you spend, the larger the effect will be, but use your Void Orbs wisely because they don't regenerate after you use them. Once they're gone, you'll have to play more cards to build these back up again.

While this image isn't a perfect representation of how I planned it to work, it should at least give you a good grasp of how it works:

Elusive - This is simply the Faerie Dragon effect. I know Ben Brode said they don't intend to make this a keyword as it would be too confusing for new players, but hey this competition is just for fun and I want it :D

Chill - Chilled minions have a shimmering light blue mist surrounding their token. The Chill takes place at the end of each player's turn. This mechanic encourages trading; it's not often that a Chilled minion will last long enough on board to accumulate a ton of damage from the Chill effect.

Warm - Examples of this currently in the game are Nerubian Prophet and Shifter Zerus. Like these cards, your opponent will not see the trigger take place. I should note that most Warm effects encourage you to hold cards in your hand, however some are still stuck in winter, and will lose value as they Warm.

Here's how Nerubian Prophet looks with the new keyword text:

The sun icon tracks the number of turns a card has Warmed. In this example, Blossoming Nymph has been kept in hand for 3 turns and is buffed to 4 health. The icon doesn't appear on a card until the Warm count is at 1 or more.

Huge shoutout to ZardozSpeaks for helping me with this graphic!!

Blessing of the Ancients:

Mechanics:

Enchant: When you play a card with Enchant, it will immediately give the next minion you DRAW (not summon nor play) a little bonus! Careful though! You may not draw the card you want to Enchant, so build your deck wisely!

Stabilize: Since Battlecries occur WHEN minions are played (not after), Battlecries will occur even if you can't pay the Stabilize cost (the same goes for Enchant). Note that Elementals with Stabilize will trigger "If you played an Elemental last turn" effects EVEN if you didn't pay the Stabilize cost because you technically did play the Elemental!

Stabilize is all about playing with your mana expenditure in order to get the optimial result! Sometimes you need to force yourself to pay the Stabilize cost to get the minion's body, but sometimes you don't want to pay it in order to just get the Battlecry/Deathrattle effect for the cheapest cost in order to play other important cards as well. This can open up for a lot of skilled plays as the usual ordering of cards is largely tampered by creating the optimal result from Stabilize cards.

Note: Cards that summon random minions (e.g. Evolve and Devolve) cannot summon minions with Stabilize, similar to how Quests can't be produced randomly. This is for obvious balancing reasons.

Flavour:

Enchant: Dalaran houses some of the most skilled sorcerers in Azeroth. Some of these guys specialize in Enchanting items and even people, making them stronger (and more stylish) than ever before!

Stabilize: While Enchanting minions are quite adept in their studies, some disciples of Dalaran are quite...inexperienced with handling spells. Sometimes, these foolish beings try to attempt the most powerful spells with little mana, and they end up injuring themselves after they fail to Stabilize their spells.

 So, how does this mechanic work? Well, X is replaced with something, such as "Murloc" or "Secret". Let's suppose I play a Dragon with Dragon Exhibit, if I control no other dragon, the ability will activate. Unlike Battlecry, Exhibit triggers after the minion is played, so they can affect themselves. When you are holding an Exhibit card, it will have the Yellow Glow if the Exhibit can trigger.

Village Forgemaster

It wouldn't be a proper Hallow's End without a heaping dose of terror! Fear is the set's new keyword that temporarily reduces a minion's Attack. Like Freeze, it expires at the end of the turn after which that minion could make an attack. So apply Fear to an enemy on your turn, it goes away at the end of your opponent's next turn. This effect can help slow down an aggressive opponent, or take the teeth out of a larger threat!