Slay The Spire is a card game. Well, you have a deck of cards and attack/defend with it, but your opponents have simple rules: attack/defend/status/buff. You know what they are going to do on their next turn, so can plan your strategy accordingly.
On the map screen, there are branching paths and you can see what each room contains. There can be regular battles, an elite battle, an event, resting spot, shop, or random.
You can acquire coins, cards and relics which you use to get stronger. You definitely need to make sure you are making good progress, because at the end of each Act is a strong boss and the difficulty ramps up in the next Act.
You start with 10 cards in your deck, and for each enemy you defeat you get to add one card in your deck. Relics can be found for permanent bonuses and these really help out along with potions. Relics can give you large benefits, but since they are often randomly given, they sometimes don't work that well with your deck. Adding cards isn't always a good idea because it reduces the chance you will draw any other card. Certain cards work well with each other, so you need the right cards in your deck, and a quantity that works for your strategy.
There aren't many opportunities to heal, so you have to make sure you are minimising damage taken each battle. Once you complete an Act, then you are fully healed. You can recover a percentage at the rest spots, but I think it's vital to use the smithing option instead where you can choose to upgrade a card. Upgraded cards are a stronger version of the card, so will have a stronger effect, or lower energy cost.
You usually have 3 energy per turn, and each card has a cost, usually 0-3. Once played, they go into the discard pile. When your deck is empty, then the discard pile is reshuffled into your deck. There is a separate “exhaust” pile which some cards go into which is only returned at the end of the battle.
The events you come across give you multiple choice options which can be a range of positives, or a range of negatives. You can gain many relics here, or restore health or coins, but you can also lose health or coins. You can also pick up some useless/harmful cards so it's always a gamble going down a path with these events. It's obviously risk vs reward. To get rid of the cards, you visit the shop but you can only get rid of 1 card per time, and it's pretty costly, and increases in cost as you use the service.
In battle, taking advantage of statuses and powers is vital for certain enemies, especially the bosses. status decrease their counter each turn, so “1 weak” means it will last one turn. Stacking the same statuses just increases the turn length rather than multiplying their effect. Powers stay for that battle, so boosting your strength by 1 remains each turn. The statuses are “Weak” – reduces attack, “vulnerable” – increases damage, and “frail” – reduces block.
Some bosses seem to require a certain strategy. So some may increase their strength per turn, so you need to go more offensive to take them down early. If you have built a defensive deck, then you don't have much of a chance. I felt it suddenly became unfair with some Act 2 bosses (such as The Collector) or all of the Act 3 bosses. Some of these bosses will attack you with one or more status effects then the next turn perform a powerful attack. When they have halved your armour, then attack you for half your health; it is extremely unfair. If you do have loads of armour cards in your hand, playing them all can still mean you take massive damage.
The different characters all have a different set of cards. So “Ironclad” is about attack. “The Silent” character is about poison and defence. The robot “Defect” is about creating orbs which attack or defend at the end of your turn.
When you are defeated, you are awarded experience which unlocks new cards and relics. This encourages you to keep replaying and can encounter new items.
There's a Daily Challenge mode which gives you set rules. The Ascension mode allows you to set your own rules.
I had a lot of fun with Slay The Spire. Each character felt different, and the cards seemed balanced well. The game felt tough, but rewarding to defeat the standard enemies. Many of the bosses felt unfair, and they often had too much health and insane attacks. This was a massive negative for me, because you end up playing for around an hour, only to have your efforts thrown away unfairly in one battle.