# Deck Building Tips: Is a Smaller Deck Better? We Played 130,000 Climbs to Find Out

> Is a smaller deck better in deck-building games? We tested 130,000 climbs: skipping cards cleared 4.9%, adding them 34.8%, adding and removing tens 40.9%.

- Source: https://yesthisgame.com/blog/deck-building-tips/
- Published: 2026-11-02, updated: 2026-11-02
- Author: Yes This Game (the team that makes the games on the site)

## Key takeaways

- In our deck builder, never adding a card cleared the tower 4.9% of the time; adding a card after every fight, 34.8%.
- Adding cards and removing a 9 or 10 in every shop worked best: 40.9% of climbs cleared.
- Thin decks win when you draw a fixed hand each turn; when you draw until you stop, more good cards means more value.
- A deck of only small safe cards cleared just 25.9%: it busts less but hits weaker.
- Stopping when the bust chance passed 20 to 30% gave the best results.

**Is a smaller deck better in a deck-building game? Not always. We played 10,000 climbs of our own deck builder with each strategy, and the player who never added a card cleared the tower only 4.9% of the time, against 34.8% for a player who added a card after every fight. The best plan was to add cards and pay to remove the high ones: 40.9%.** "Keep your deck thin" is about how often you draw your best cards, and that only matters when your hand size is fixed. Below: what deck builders are, why thin decks win in some of them, our test, and nine tips. You can try every strategy yourself in [Lucky 21 Tower](https://yesthisgame.com/lucky-21-tower/).

## What a deck-building game is

In most card games you bring a finished deck. In a **deck builder** everybody starts with the same small, weak deck and improves it while playing: you add better cards, upgrade some and throw others away. Building the deck is the game.

- **Dominion** (2008), a tabletop game by Donald X. Vaccarino, made the idea popular: players buy cards from a shared market, and every card bought goes into their own deck.
- **Roguelike deck builders** moved it to video games and to a single run: you fight a chain of battles, pick one of a few cards after each win, and start again from nothing when you lose. Slay the Spire (2019) set the pattern; Balatro (2024) did the same with poker hands.
- Most of them share three choices after every fight: take a card, skip it, or remove one. That is exactly what we tested.

## Why players say "keep your deck thin"

In Slay the Spire you draw five cards a turn. If your deck has 10 cards and two of them are great, you see a great card most turns. Add ten average cards and the same two great cards turn up half as often. Removing weak starter cards, often called **thinning** , raises the chance that each draw is a good one. Taking every card you are offered does the opposite and is a classic beginner mistake in those games.

But the rule rests on the fixed hand. Change how drawing works and the answer can change. In Lucky 21 Tower you do not draw five cards: you keep drawing until you decide to strike, and your total is your attack, like in blackjack. Every card that comes out also does its job: a Shield card guards you, a Heart heals, Blaze adds damage. So we measured it instead of guessing.

## How we tested it

- **The game:** the first version of Lucky 21 Tower (November 2026), using its own rules code: 15 floors of monsters, a starting deck of 20 number cards (two aces, two of each card from 2 to 9 and two tens), one card offered out of three after most fights, and a shop after floors 3, 8 and 12 that can remove a card.
- **The player:** a program playing Leo the knight the same way every time: draw while the bust chance is at most 30%, use Peek when the total is 12 or more, drink a potion below 40% health, rest in shops when hurt.
- **The runs:** 10,000 climbs for each strategy, all on the same 10,000 shuffles, so the only difference is the deck-building choice. That is 70,000 climbs, plus 60,000 more for the risk test below.

## Results: what to add, what to remove

*10,000 climbs per strategy in Lucky 21 Tower*

| Strategy | Tower cleared | Floors beaten (avg.) | Cards at the end | Lucky 21s per climb |
| --- | --- | --- | --- | --- |
| Add a card, then remove a 9 or 10 in every shop | 40.9% | 12.4 | 28.7 | 7.9 |
| Add a card, then remove a 2, 3 or 4 in every shop | 36.2% | 12.3 | 28.6 | 7.6 |
| Add the first card offered, every time | 34.8% | 12.3 | 30.2 | 7.6 |
| Add only big damage cards (Blaze, Thunder, Star, Mirror) | 34.4% | 12.1 | 28.0 | 8.5 |
| Add only small safe cards (Feather, Shield, Heart, Bubble, Coin) | 25.9% | 12.1 | 29.4 | 5.8 |
| Never add a card (take 10 coins instead) | 4.9% | 10.5 | 20.0 | 4.8 |

![Bar chart of tower clear rate by deck-building strategy: 40.9% adding cards and removing high cards, 34.8% adding every card, 25.9% only safe cards, 4.9% never adding](https://yesthisgame.com/wp-content/uploads/2026/11/deck-building-strategies-chart.png)

Three things stand out.

1. **Skipping cards was a disaster.** The thin 20-card deck cleared the tower in one climb out of 20. Every special card in this game still counts toward 21 and adds an effect on top, so passing it up throws away free value.
2. **Small safe cards were worse than average ones.** A deck full of low cards rarely busts, but every hand ends up with a lower total, and a lower total is a weaker attack. The safe deck hit 5.8 lucky 21s a climb against 7.6 for the plain strategy.
3. **Removing high cards beat removing low ones** (40.9% against 36.2%). Each ten taken out lowers the chance that the next card busts you, which lets you take one more card more often and land closer to 21.

## How much risk to take on each draw

We also changed only the moment the player stops: strike as soon as the chance of busting on the next card is higher than a set limit.

*Where to stop drawing (a second set of 10,000 shuffles per row, adding the first card offered)*

| Stop when the bust chance is over | Tower cleared | Floors beaten (avg.) |
| --- | --- | --- |
| 10% | 30.8% | 12.2 |
| 20% | 34.3% | 12.4 |
| 30% | 34.5% | 12.3 |
| 40% | 33.2% | 12.1 |
| 50% | 30.4% | 11.7 |
| 60% | 26.6% | 11.2 |

The best zone was a bust chance of about 20 to 30%: take another card while three in four cards or more are safe. Playing scared (10%) cost almost as much as playing wild (50%). In blackjack terms, the chance of busting a hard 12 is 31%, so this is close to "always hit 11 or less, think hard from 12". The full table for real blackjack is in [Blackjack Bust Chance by Total](https://yesthisgame.com/blog/blackjack-bust-chance/).

## Nine deck-building tips

1. **Know your draw rule first.** If you draw a fixed hand each turn, a thin deck finds your best cards more often. If you draw until you stop, as in Lucky 21 Tower, every card gets played and more good cards simply means more value.
2. **Do not skip early.** A card that is only "fine" in the first fights is still better than nothing. In our test, skipping every card cleared the tower 7 times less often.
3. **Remove your worst starters, not your best numbers.** In games with a fixed hand, the weak starting cards go first. In a push-your-luck deck, the cards that make you bust go first.
4. **Balance safety and power.** A deck of only small, safe cards does not bust, but it also does not hit hard.
5. **Count what is left.** Every card drawn changes the odds of the next one. Lucky 21 Tower lets you tap the deck to see the cards still to come.
6. **Plan for the boss.** Check what the next big enemy does, such as a shell that blocks part of every hit, and pick cards that answer it.
7. **Spend coins where they change the most.** A card removal or a charm helps every fight that follows; a potion helps once.
8. **Stop at a set risk.** Pick a limit (20 to 30% worked best for us) and keep to it instead of deciding by feel.
9. **Play many short runs.** Deck builders are made for losing and trying again: each run teaches you which cards really matter.

Want to try it? [Lucky 21 Tower](https://yesthisgame.com/lucky-21-tower/) is free in your browser. Since this test it has grown to 30 floors in three worlds, with a door to choose on every floor, card upgrades and six heroes; the card rewards and the shop that removes cards work the same way.

## Frequently asked questions

### Is a smaller deck better in deck-building games?

Only when you draw a fixed number of cards each turn, as in Slay the Spire: then a thin deck finds its best cards more often. In a draw-until-you-stop game like Lucky 21 Tower, adding cards won clearly: 34.8% of climbs cleared against 4.9% for never adding.

### What is deck thinning?

Removing weak cards from your deck so that each draw is more likely to be a good card. It is usually done in shops or events that let you remove a card.

### Should you skip card rewards?

Skip a card only when it would make your deck worse at what it already does. Skipping by habit is a common mistake: in our test it cut the clear rate about seven times.

### Which cards should you remove first?

In fixed-hand games, the weak starting cards. In push-your-luck games, the high cards that make you bust: removing 9s and 10s gave our best result, 40.9%.

### What was the first deck-building game?

Dominion, a tabletop game by Donald X. Vaccarino published in 2008, is the one that made the genre popular. Video games such as Slay the Spire later turned it into single-player runs.

## Games in this guide

- [Lucky 21 Tower](https://yesthisgame.com/lucky-21-tower.md): Play Lucky 21 Tower free: draw cards, get close to the magic number and strike. Climb 30 floors in three worlds, build your deck, unlock six heroes.
- [21 BlackJack](https://yesthisgame.com/21-blackjack.md): Play blackjack free online with $1,000 in practice chips: beat the dealer to 21 without real money. Rules, a simple strategy and tips. No download.
- [BATTLE JACK 21](https://yesthisgame.com/battlejack.md): Play Battle Jack 21 free online: pick a champion, draw cards towards 21 and strike. Exactly 21 wins the battle, over 21 does no damage. No download.