How to Tetris

25: BT-STSD

Tutorial Videos

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The Basics

BT-STSD, or Gemini, is a spliced STSD with 3 T-spin doubles:

Diagram Set 25-1

Here is how to complete it:

Diagram Set 25-2
12
Starting field.Make the first T-spin double.
34
Then the second T-spin double.And the third.

Common Mid-Game Chances

Constructing it mid-game is straightforward because of many common situations.

1. General Ways

    Here are memorizable ways to construct its parts using the permutations of certain pieces:

    Diagram Set 25-3
    AB
    CD

    2. Sky Prop Upgrade

    Sky Props provide the easiest and most common mid-game situation to build a BT-STSD.

    I often encourage players to first learn to create BT-STSDs during 9-0 stacking. This is because you only have to manage one side of the stack.

    Diagram Set 25-4
    12
    You can easily upgrade step 1’s Sky Prop to a Gemini by stacking I and L this way.

    Or, like in the above diagram, you can spot this situation (which I call a ‘Boot’ as it looks like a boot) and top the BT overhang over it.

    Constructing the base (left sides, below) is tricky. However, here are some common piece combinations:

    Diagram Set 25-5
    AB
    CD
    Upstack to make the BT-STSD.
    The left side of the BT-STSD can be constructed in many ways. However, they are finite and can be memorized.

    3. Mid-Lane Chances

    When the player has gotten accustomed to creating BT-STSDs during 9-0 stacking, they can switch to spotting it during the mid-lane, when the garbage hole is away from the corners.

    This is more challenging now, as there are 2 sides of the stack to manage (left and right sides):

    Diagram Set 25-6
    12
    Once you can construct BT-STSDs during  7-2 stacking easily, transition to recognizing mid-lane mid-game chances.

    4. Freestyle BT-STSDs

    Only when one has familiarized themselves with BT-STSDs can they freestyle it:

    Diagram Set 25-7
    AB
    Transition to non-Sky-Prop mid-game freestyle chances like the above. This takes lots of practice.

    Advanced

    BT-STSDs have advanced variations, which are unfortunately completely impractical.

    1. Spliced BT-STSDs

      You can insert extra T-spins into a BT-STSD. Here is an extreme example, often used by Yakine and me. It is called Scuti:

      Diagram Set 25-8
      12
      Spot this common mid-game chance.Put O on it and freestyle the rest. This inserts a T-spin inside the BT-STSD.

      I invite players to experiment with this egregiously impractical setup for fun.

      In a Nutshell

      BT-STSDs, like DT-STSDs, are rare to create mid-game. They upstack heavily and can be dangerous if one is heavily pressured. However, its most common situation, a Sky Prop upgrade, can sometimes be practical.

      Pros and Cons
      ProsProvides 3 T-spin doubles, which is a substantial burst of damage.

      Has many easy-to-spot mid-game situations, such as upgrading from Sky Props.

      Ends in a clean T-spin double.
      ConsHas a shape as complex as BT Cannons, making them difficult to freestyle mid-game.

      Upstacks dangerously and renders you susceptible to spikes while building it.