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If you read about any TCG strategy like our latest article about Mythical Slab, you may come across the term “deck thinning”. But what does it mean and how important is it really?
Thinning is the act of removing a card from your deck so that you are more likely to draw into the cards that you really want in a subsequent action. Importantly, it isn’t just the act of removing any card. It only improves your chances when you’re removing a card that you actively don’t want! The power of this action can be quite dramatic, but more commonly it will only provide you a subtle advantage and dictate how you should technically sequence some cards.
Let me give you some (admittedly contrived) examples and counter-examples:
Example 1 : 2 Cards Left in the Deck
The game is nearly over. You just have to survive one turn and hope to draw your Sabrina so that you can snipe one of the weak Pokemon on your opponent’s bench. You have two cards left in your deck. One of them is the Sabrina, and the other is a basic Pokemon. Fortunately, you have just drawn a Poké Ball.
By using the item now, you will put the basic Pokemon in your hand and guarantee that you’ll draw your Sabrina next turn. You can thin the deck and increase your chances of winning the next turn from 50% to 100%. That’s a pretty big effect, but this isn’t a common scenario.
Example 2: Looking for an Evolution
This one is similar to the first example but more common. Here you have your basic in place (perhaps a Koffing) and you’re hoping to draw the Stage 1 to evolve it (Weezing). In this and all of the rest of the examples, let’s assume that you have a Poké Ball and a Professor’s Research. Since we’re looking to draw a non-basic as soon as possible, it will be best to remove the cards that we don’t want to draw from our deck before we play the Professor’s Research.
If this is the first turn of the game, thinning the deck improves our odds by a whopping ~1.8%! OK, that’s literally the same play as in Example 1, but you can see that in the more common scenario, the actual improvement to our chances is very minimal.
Example 3: Filling the Bench
You only have one of your 7 total basic Pokemon on the board and none in hand. But you do have a Poké Ball and a Professor’s Research. At this point, you really need to find any other basic, but it would be even more preferable to find two so that you can fill out your bench and power up your Pikachu EX. Should you play the ball first or the research?
Well, it turns out that this is a case where you actually want to play the Professor’s Research first. Removing a basic Pokemon from the deck by playing the Poké Ball first would be removing one of the cards that you’re hoping to draw with your Professor’s Research. Remember that we only want to remove cards we don’t want to draw!
Assuming that this is the start of the game, it turns out that the research-first sequence is just a little bit better at finding more than one basic Pokemon. How much better, you ask? Not much. The odds that the Professor’s Research draws at least one basic Pokemon jumps from ~60% to ~66%. But technically correct is the best kind of correct!
Example 4: Getting to Moltres ex
The game has just started and you’re playing a deck that leverages Charizard EX’s powerful attack as a win condition and Moltres EX’s single energy attack to power up the Charizard as fast as possible. When you look at your hand you see all three pieces of the Charmander evolution, a Poké Ball, and a Professor’s Research. You have to start with the Charmander, but you’re going to try to draw a Moltres EX as fast as possible. You have 5 total basics in your deck, including the 2 Moltres EX: how can we best do this?
Well, this is going to get complicated. Because you’re looking for a specific basic, both playing the Professor’s Research or playing the Poké Ball has a chance of outright success and a chance of thinning the deck for the other card. This scenario, and many like it, are in the “shut up and calculate” class of problems and there is no golden heuristic to guide you here. The order does matter, but, fortunately, the order doesn’t matter a lot. Most of the time you will be making these decisions at the beginning of the game, like in this scenario. And it’s likely that the problem will have the same solution as this one. So when in doubt, play Professor’s Research first and Poké Ball second.
For those of you who really must know the specifics, this exact scenario is ~56.5% to get at least one Moltres EX if you Poké Ball first, and ~59% to get at least one Moltres EX if you play Professor’s Research first. A mere 2.5% difference in outcome.
It’s also worth noting that this is the exact same math for the scenario where you have a stage 1 in hand and are looking for the specific basic that it evolves from.
Conclusion
Deck thinning is clearly a very mathy subject, and it’s often misunderstood. And while it can have some really big consequences in a narrow range of cases, as you can see, it’s not a particularly big effect in most common scenarios. If you choose to pay attention to these kinds of technical sequencing details while playing, just know what you’re trying to remove, or not remove, from your future draws. If you do that, it should be pretty intuitive what sequence you want to use. And if you get it wrong? Well, it probably wasn’t that wrong anyway, so don’t sweat it!