There are 264 cards in War of the Spark. Additionally, there were 10 cards exclusively available in the Planeswalker decks released with the set, and one Buy-a-Box promo card, which was available if you bought a sealed booster box at the release.

These additional cards are labeled 265/264 through 275/264.

Breaking it Down

War of the Spark contains a total of 15 Basic Lands, 101 Commons, 80 Uncommons, 53 Rares, and 15 Mythic Rares.

The exclusive cards featured in the Planeswalker decks included two Mythic Planeswalkers, two Rares, two Uncommons, two Commons, and two Common Guildgates, which are Land-Gate cards. These Enter tapped and tap for two colors, each representing one of the Ravnica guilds.

Basic Lands

There are three Basic Lands for each color in War of the Spark, for a total of 15 cards.

There are five of them (card numbers 261, 252, 258, 254, and 264) which, when laid out in that order, create a single piece of panoramic art.

Commons

War of the Spark was a set about Nicol Bolas' dread desire to harvest Planeswalker sparks, the magical energy allowing them to travel among planes.

That means the set had the largest number of Planeswalkers in a set by a massive amount; most sets have three, all at Mythic Rarity. War of the Spark had 39, including the two from the Planeswalker decks and the Buy-a-Box promo, with rarities going as low as Uncommon.

Each Planeswalker had a corresponding spell, a card which is the sort of thing that the specific Planeswalker might cast. One of the best-selling and most useful Commons in the set is tied to the Planeswalker Kaya Cassir, a Ghost Assassin Planeswalker.

That card is Kaya's Ghostform, a Enchantment-Aura which you can attach to a Creature or Planeswalker you control. When that Creature or Planeswalker dies or goes into Exile, you can return it to the Battlefield under your control.

Uncommons

The sheer volume of Planeswalkers in War of the Spark meant several of them show up at Uncommon, which had never been done before.

One of the best is Narset, Parter of Veils, a Planeswalker which Enters with five Loyalty.

She has a static ability which stops your opponents from drawing more than a single card each turn, and she has a -2 ability which allows you to look at the top four cards of your Library, reveal a noncreature, nonland card from them, and put it your Hand, putting the rest on the bottom of your Library.

It wasn't all Planeswalkers, though. Pledge of Unity is a Instant which puts a +1/+1 counter on each Creature you control, then you gain a life for each Creature you control as well.

Rares

The 53 Rares in War of the Spark include some really impactful cards, but the most influential is Bolas's Citadel, an Artifact for .

It allows you to look at the top card of your Library at any time, but more importantly, it lets you play cards off the top. If you cast a spell, you pay life equal to the mana value of the card rather than a mana cost.

Additionally, you can tap it and sacrifice 10 nonland Permanents to deal 10 damage to each Opponent, which is powerful.

Mythic Rare

It stands to reason that the 15 Mythic Rares in the set are quite powerful, but few are quite as strong as Liliana, Dreadhorde General. This angry Planeswalker costs and Enters with six Loyalty.

Her static ability draws a card every time you have a Creature die, and her +1 ability makes a 2/2 Zombie Creature Token.

Her -4 forces everyone, including you, to Sacrifice two Creatures, and her -9 Ultimate Ability forces every Opponent to choose one Permanent of each type they control and sacrifice the rest, which is brutal.

One More Worth Mentioning

The Buy-a-Box promo was only available when you bought a box and later in a Secret Lair drop.

Tezzeret, Master of the Bridge is a Planewalker with five starting Loyalty.

He makes Creature and Planeswalker spells you cast have Affinity for Artifacts, which means they cost less for each Artifact you control.

Add to that a +2 ability which deals damage to each Opponent equal to the amount of Artifacts you control, and you gain that much life, and you already have a strong Planeswalker.

His -3 lets you bring an Artifact back from the Graveyard to your Hand, and his -8 Exiles the top 10 cards of your Library, then puts all Artifacts Exiled this way onto the Battlefield.

Final Answer

How many cards are in War of the Spark? There are 264 set cards, with 10 additional cards from the Planeswalker decks, plus one Buy-a-Box promo card, for a total of 275/264 cards.