You cast cards using Power in Eternal, and you gain Power by playing various Power cards. The five basic Power cards are Justice Sigil, Fire Sigil, Shadow Sigil, Time Sigil and Primal Sigil.
In addition to providing one Power, most Power cards provide one or more Influence. There are five types of Influence, corresponding to the five factions. Most cards have both a Power cost, shown in the top left corner, and an Influence requirement, shown as faction symbols to the right of the cost. However, unlike Power, Influence is not used up when a card is played. For example, if you only have one Time influence, you can still play multiple cards that require a Time Influence in one turn, as long as you have enough Power to play all of them.
The Depleted keyword is specifc to power cards, and causes them to not give power on the turn they are played.
Types of Power Cards
Several cycles of power cards have been released, each with different properties. Each cycle comprises either a set of five cards, one for each faction, or a set of ten, one for each faction pair.
In addition to these cycles, there are Sigils, the basic power cards, and a small number of faction-neutral power cards which either do not provide influence, or conditionally provide an influence of your choice.
Sigils
Sigils are the basic power cards. There are five of these, one for each type of influence. Sigils are the only card of which more than four copies can be added to a deck in constructed play.
Seats
Seats are a cycle of 10 power cards from The Empty Throne. Each Seat provides two different influence, but is Depleted unless the player has a Sigil in their hand.
Monuments
Monuments are a cycle of 5 power cards from The Empty Throne. These provide one influence and are Depleted. They all have Transmute 5 - if you reach 5 power before playing a Monument, it will change into a specific Unit or Weapon with cost of 5.
Banners
Banners are a cycle of 10 power cards, released across The Empty Throne and Omens of the Past. Each Banner provides two different influence, but is Depleted unless the player has a unit in play.
Waystones
Waystones are a cycle of 5 power cards from The Dusk Road. Each provides one influence, and has an additional effect that is activated if you have at least four of that type of influence after playing it.
Crests
Crests are a cycle of 10 power cards from The Dusk Road and The Fall of Argenport. Each provides two influence, is Depleted, and has the Scout keyword, allowing you to look at the top card of your deck, and put it on either the top or bottom.
Standards
Standards are a cycle of 5 power cards from The Fall of Argenport. These provide one influence and are Depleted. These all have Transmute 5 - if you reach 5 power before playing a Standard, it will change into a specific Fast Spell with cost of 2.
Other Power Cards
As of Into Shadow, there are four faction-neutral Power cards: