Undercroft Deckbuilder Roguelike Combat Guide: Turns, Block, Potions and Winning Fights

Quick answer

Undercroft battles are turn-based card fights. On your turn you play cards from your hand one at a time: attack cards deal damage to enemies and Guard/Block cards build block. You can tap a potion whenever you need it, and potions are free to use. Once you have played what you want, you end the turn and the enemies take their actions. The fight ends when every enemy is defeated, and winning hands you a post-fight pick such as adding a card to your deck.

• Play cards from your hand one at a time — attacks deal damage, Guard cards build block.
• Block absorbs the damage enemies deal; when attacks get through, you lose HP.
• Tap a potion to use it mid-fight — potions are free to use.
• End the turn when you are done, and the enemies act.
• Defeat every enemy to win the fight, then take your post-fight card pick.

How a turn works

Undercroft: Deckbuilder Roguelike is tagged RPG / Turn-based RPG on its official Roblox page, and a battle plays out exactly that way: you take a turn, the enemies take theirs, and the rounds alternate until one side is finished. A player who recorded an early run described the game as similar to Slay the Spire — but “not exactly”, with its own different UI — so expect this style of fight rather than an identical copy.

One round of battle

1. 01

   Play your cards

   Play cards from your hand one at a time. Attack cards deal damage; Guard/Block cards build block.

2. 02

   End the turn

   When you have played what you want, end the turn.

3. 03

   Enemies act

   The enemies take their actions. The block you built absorbs their hits, and any damage that gets through costs HP.

Your next turn then begins the same way, and the rounds keep alternating until every enemy is defeated.

The real decisions sit inside the first stage: whether the attacks in your hand can finish an enemy this turn, and how much block — or a potion — you want behind you before the enemies act.

Which cards to play

Attack cards are your damage. In an early run played as a knight, the attacks cycling through the hand included Slash, Kick the Fallen, Hammer Down and Rebuke — the exact names you see depend on the deck you have built. Guard cards are the other half of the hand: they add block instead of damage, and doubling up on them was a normal play when a dangerous enemy turn was looming.

Cards also carry text effects rather than raw numbers. One card in that run read “Apply three exposed”, and another applied an effect described as “enemy loses might this turn”. Read what a card actually does — and what it costs — before you play it or take it as a reward: the run also surfaced offered cards with downsides baked in, like “Burn away, lose six HP”, and one that traded HP for a large block gain.

For looking up individual cards, see the cards list. The deckbuilding guide and the deck builds page cover the deck-building side of combat.

How block works

Block is damage prevention. Guard/Block cards grant block, and that block absorbs the damage enemies deal. With block up, the run's narrator took no damage at all — “we're not taking damage” — while unblocked hits visibly tore into HP instead (“Oh, that hits hard”). Fights can swing hard enough that you need a Guard played “so we don't actually just straight up die”, because an unblocked stretch can put you near death.

One caveat from the same run: enemies can have special abilities that interfere with your plays. In one fight, a Guard was stopped by an enemy special ability that was “blocking us from blocking it”. A Guard does not always resolve the way you planned, so watch what enemies do, not just what you play.

Potions: the free mid-fight rescue

Potions are used by tapping them — the game prompts you to “tap the potion to use it” — and they are free to use, so drinking one in battle costs you nothing. The only requirement is carrying them: a potion can only bail you out if you picked it up beforehand.

In practice they are the emergency button. The run's narrator drank potions mid-fight to survive heavy hits, including through the Rat King fight, where a potion came out right as the damage turned lethal. They cost nothing to use — the real limit is how many you are holding — so the useful habit is having a few before a hard fight starts, not saving them for a perfect moment.

Statuses you will see: Expose, Might and Stun

• Expose — a status your cards can apply; it showed up on card text in the run (“Apply three exposed”).
• Might — a two-sided stat: both you and the enemies gain and spend it, and some effects move it directly, like making the “enemy loses might this turn”.
• Stun — enemies can end up stunned. When a group was stunned in the run, the player stopped attacking it and moved on; no more damage was needed there.

How the fight ends

A fight is won by defeating the enemies — and it can end abruptly. The narrator kept lining up attacks, then realized “Oh, never mind. I won already”: the last enemy had dropped before the turn's plan was spent. Wins can land mid-turn rather than at a tidy stopping point.

Winning hands you a pick right after the fight. In the run, that was a choice like adding a card — or a copy of a card — to your deck. Cards can also reward the win itself: one read “When you win a fight, heal six”, so some decks recover HP just for finishing fights.

You can live through hits that look lethal — the narrator's reaction to surviving one was “You're not dead yet?” — so don't write off your chances when a big hit lands. For what happens when a run ends in death, see the revives guide. For enemy-specific approaches — including fights like the Rat King, which this run survived on mid-fight potions — the bosses guide is the dedicated page.

Habits worth keeping

Tips

01

Read the card text

Some cards carry costs with their effect — one in the run read “Burn away, lose six HP”, and another traded HP for a large block gain.

02

Guard before the enemy phase

Block absorbs the hits enemies deal. With block up, the run took no damage; without it, heavy hits tore straight into HP.

03

Spend potions when the fight turns

Potions are tapped to use and free to use — this run survived the Rat King fight on mid-fight potions. You can only use the ones you are carrying.

04

Let a stun close a group out

When enemies were stunned in the run, no more attacks were needed on them and the turn went elsewhere.

05

Expect the sudden win

A fight ends the moment the last enemy drops, even mid-attack, and the post-fight pick — like adding a card to your deck — follows right away.

Where to go next

• Deckbuilding guide — building the deck you take into fights.
• Cards list — what individual cards do.
• Deck builds — whole-deck approaches to combat.
• Heroes guide — heroes in the game, including the knight played in this guide's source run.
• Bosses guide — enemy-specific fight notes.
• Runs guide — how single fights fit into a full run.