Disk of Circadia
Disk of Circadia is the last path acquired through normal leveling. This is probably for the best, as while it might not be the most complicated, it is probably the toughest to play. Disk of Circadia is the most "active" Path, requiring a decision on when to activate it and what to do when it's activated, as well as having a constant effect on the board. All of these decision points can make it not only intimidating to new players, but difficult to use correctly for more experienced players. I find myself making more mistakes playing with, or against, Disk of Circadia than any other path. So, how do you use it?
What are the requirements?
All of the other paths have an obvious way by which they generate card advantage; this is not the case with Disk of Circadia. The first trigger of the Path actually causes you to discard a card. Why am I playing this? So you can draw cards! The second activation of the Path allows you to divination 2 and draw. So far all we have is some expensive card filtering.
To really make use of Disk of Circadia you need a way to break the symmetry. The most common way to do this is to either play cards you really want to discard, or that you don't care if you discard. Huh? You may want to discard large minions, like Indrik Beast, to set up for a Hopeless Necromantic, or you might not care if you discard a Born Again, Parsa Recruit, or purple item. The second approach actually allows you to generate card advantage.
The other way to break the synergy is to have no cards to discard. Decks that can do this effectively draw an extra card every two turns, which is way above the baseline. This is possible in some Aggro strategies, which may also benefit from the Slayer 1 provided by Day.
Disk of Circadia is also the only Path directly tied to your Power. Switching states requires you to activate your power. Because of this, it is almost a necessity to use a Power that does not require a target.
What makes it good?
Disk of Circadia performs best when a deck is specifically crafted to benefit from the discard effect. Or, at the very least, not be punished by it. This pushes it towards graveyard synergies.
What makes it bad?
It buffs your opponents minions! The Day side gives Slayer 1 to all minions. Players always forget this, and it really can complicate turn sequencing.
Changing states requires a Power activation. If you want to be swapping states constantly, this costs a lot of mana, which might be better used to develop your board.
What archetypes?
Disk of Circadia is most commonly used in conjunction with Hopeless Necromantic in Reanimator decks. These can be classified anywhere from Midrange to Control to almost combo in the case of GB Necromantic.
Alternately a deck like OP Aggro can make use of the Disk. I think Disk Aggro decks have potential, but are currently under explored.
What Powers?
Disk of Circadia requires Power activations to function. In order to guarantee you can flip states it is best used with a Power that does not have an activation requirement: Mend, Smite, or Foresight. Foresight is a bit underwhelming as half the Disk activations already grant Divination 2. This leaves Smite and Mend. Midrange and control decks will most likely get more value from Mend, while Disk Aggro gets the prize as the only deck where playing Smite is probably correct.
Playing with Disk of Circadia
Have a plan, and stick to it. Disk of Circadia can be very punishing when you change your mind mid turn. You may also have to plan 1-2 turns ahead to ensure you have the card you want to discard at the right time.
The Slayer 1 from Day affects both players. Look for ways you can use this to your advantage. Sometimes you want your minion to die.
Save cards to discard.
Don't get predictable. Disk can be very difficult to play against when your opponent is unsure what state it will be in on from turn to turn.
Playing against Disk of Circadia
Don't forget about Slayer.
Always know what Hopeless Necromantic will return and have a plan in advance on how to deal with it. If you have an answer, initiate the trade, otherwise force your opponent to.
Look for patterns in their activations. You may be able to gain an advantage if you know what state the Disk will be on your next turn.
Try and force your opponent into awkward plays. Powers are inefficient, forcing their activation gives you a chance to get ahead.
Night and Day
Disk of Circadia is actually one of the more powerful Paths. It has a very unique effect, which gives it some of its power, but also makes it a bit niche. It is currently under explored and as the player base and card pool expands so will the use of the Path.
On the flip side, our next Path is both the last and the least. While Fires of Creation has an interesting effect on the game, it also has some severe drawbacks that limit its power. Often times decks built to use Fires will fair better using a different Path. Why? Find out next time!