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What is FOUR?

FOUR (FOUR) is a quick-reference guide to Tetris strategy, focused on the setups players actually use rather than general explanation. Its stated approach is "No fluff. Just things you need to know," and the page evidence bears that out: the site is organized around named techniques, each with a short description of what it does and when you'd use it.

What it covers

The content is split between openings and mid-game methods.

Openers are starting setups keyed to the order of pieces in your first bag. Examples from the site include TKI, a popular opener that sends a T-Spin Double immediately; DT Cannon, a TSD → TST opener used with an early L-S or J-L; and the Perfect Clear Opener, described as having an 84.64% chance of a perfect clear if you hold I. Others listed are Hachispin, MKO, C-Spin, BT Cannon, Mr. T-Spin's STD and Albatross.

Methods are mid-game setups, such as T-Spin Triple, Fractal ("double dagger"), Imperial Cross, Parapet, Kaidan, STMB Cave, STSD, Shachiku Train and Polymer T-Spins. Each entry names the setup and gives a one-line sense of its shape or purpose—for instance, Parapet is described as a donation TSD/TSS technique named for how the J or L covering the hole resembles a parapet.

Who it suits

This is a reference for players who already know Tetris terminology—bags, holds, T-Spins, donations—and want to look up a specific opener or setup mid-practice or mid-conversation. It is less useful for someone learning the game from scratch, since the entries assume familiarity with the underlying mechanics.

A practical next step

Pick one opener that matches a start you see often, such as TKI for a straightforward early TSD, and drill it in a practice mode until the piece placement is automatic. Then use the Methods section when you want a mid-game option to follow it up.

Which Tetris opener should I choose based on my first bag piece order?

Choose based on the pieces you actually get in your first bag, not on a single "best" opener. The practical rule is to match the opener to the early pieces it requires, and to have a fallback for bags that don't fit.

FOUR lists openers by their starting conditions, which is the right way to pick one:

How to decide in practice

1. Look at your first bag and identify the key piece the opener needs (often I, L, J, S or Z).
2. Pick the opener whose required start you have; if none fit cleanly, default to a simple TSD opener like TKI rather than forcing a complex setup.
3. Learn one or two openers well before adding more. Recognising the start matters more than knowing many names.

As a next step, practise reading your first bag and naming which opener it enables before you place a piece. That habit, rather than memorising every setup, is what makes opener choice fast in real games.

How do I set up a T-Spin Triple mid-game?

Use a T-Spin Triple (TST) mid-game by building one of the standard TST → TSD shapes and sliding the T into the three-row notch it leaves. The TST is the first hit; the follow-up T-Spin Double is the second. On FOUR, the mid-game method listed for this is Triple Double (TD), described as a TST → TSD setup, alongside the DT Cannon, which is a TSD → TST setup first outlined by TKI.

Practical setup sequence

1. Reserve a three-row vertical notch with an overhang above it, so the T can enter sideways and rotate into the slot.
2. Stack the surrounding columns flat on both sides; uneven surfaces are what usually turn a planned TST into a messy stack.
3. Keep the overhang piece late. Build the body of the shape first and place the piece that creates the overhang only when the T is close in your queue.
4. Check your next pieces before committing. If the T is far away, the notch becomes a liability in versus play.
5. Follow through with the TSD the shape leaves behind, rather than flattening the residual overhang immediately.

Choosing between the common mid-game routes

A concrete scenario

Suppose you are mid-game with a flat 9-wide field, a two-deep well on the right, and an S piece in your next queue. Rather than filling the well, hang the S so it leaves a T-shaped gap beneath it, then stack the left side to match height. When the T arrives, rotate it into the notch for the triple, then use the remaining gap for the double. If the T is more than a few pieces away, place the S flat and abandon the setup — a half-built TST is worse than a clean stack.

Decision criterion

Commit to a TST only when three conditions hold: the T is within roughly the next three to four pieces, the surrounding columns are within one row of each other, and you are not under immediate garbage pressure. Otherwise, use the TSD-first DT Cannon or a simpler double setup and keep your stack low.

What is a perfect clear opener and how likely is it to succeed?

A perfect clear opener (PC opener) is a Tetris opening whose first-bag setup is designed so that, after sending an attack, the remaining board can be emptied completely. Clearing the whole board is the strongest attack in guideline Tetris, which is why players build their first pieces specifically to make it possible.

How it works in practice

You place your first bag in a fixed arrangement, fire a spin attack (often a T-Spin Double), and then fill the leftover gaps with the next pieces. The catch is that the clear depends on which pieces arrive next, so the opener is a bet on the coming bag rather than a guaranteed result.

On FOUR, the Perfect Clear Opener is described as having an 84.64% chance of a perfect clear if you are holding an I piece. That figure applies to that specific setup and hold condition, not to PC openers in general—other openers listed there, such as MKO, offer a 33% perfect clear chance with a fallback into T-Spin Doubles.

Choosing between openers

A concrete case: if your queue gives you an early I and you are comfortable with the hold, the PC route rewards you with a board wipe; if the I comes late or you need guaranteed damage, an opener like TKI or DT Cannon sends a TSD from the first bag without relying on luck.

As a decision rule, pick the opener that matches your queue and your appetite for risk, and learn the fallback continuation for when the perfect clear fails—that fallback is what separates a useful PC opener from a gamble.

How does a donation T-Spin technique like Parapet or Shachiku Train work?

A donation T-Spin uses one piece to build the overhang that makes a T-Spin possible, rather than stacking the overhang yourself. You place a piece (often J or L) so it covers a gap and creates the notch a later T can slot into, then "donate" that piece to the setup and cash in the T-Spin afterward. On FOUR, Parapet is described as a donation TSD/TSS technique named for how the J or L covering the hole resembles a parapet, and Shachiku Train is listed as a donation TSD → TSD method—one donation that feeds a second T-Spin Double.

What the two examples do differently

The trade-off is board cost: the donation piece is spent shaping the stack, not clearing lines, so a failed or abandoned setup leaves an awkward overhang. Parapet is the more flexible single-hit option; Shachiku Train asks for more commitment in exchange for two T-Spins.

Next step: In a practice session, set up Parapet first and watch whether the donated J/L leaves you a clean follow-up if the T never arrives. If that recovery feels comfortable, try Shachiku Train's two-stage chain.

What is an STMB Cave and when should I use it?

An STMB Cave is a mid-game T-Spin technique in which you hang an S or Z piece over a three-wide column to create the shape for a T-Spin Double. It is one of the setups FOUR lists among commonly used mid-game techniques, alongside donation T-Spins like Parapet and Kaidan and multi-step setups like TST and Imperial Cross.

When it fits

• You have an S or Z piece you would otherwise bury. The hang turns an awkward piece into the roof of the cave rather than garbage in your stack.
• You can build or already have a three-wide column. The cave needs that well to form the T-Spin Double shape, so it suits a board where a narrow well is open and reachable.
• You want a mid-game attack, not an opener. Unlike TKI or DT Cannon, which are built from the first bag, the STMB Cave is a technique you apply once the game is underway and the board has taken shape.

Trade-offs

The setup commits a piece to a specific overhang, so if the follow-up T piece does not arrive in time, you may need to dismantle the shape or take a weaker clear. Compare it with donation T-Spins such as Parapet, which use a J or L over the hole: those are often easier to slot into an existing stack, while the STMB Cave asks you to plan around a three-wide column. If your board has no clean column, a TSD → TST setup like the DT Cannon is usually the more practical route.

A concrete example

Suppose your stack has a three-wide gap on the right and you draw an S piece with no good flat placement. Hanging the S across the top of the gap sets up the cave; when the T arrives, you rotate it into the overhang for a T-Spin Double. If the T is delayed, check whether a donation T-Spin elsewhere on the board can absorb the piece instead.

As a next step, practise recognising the three-wide column and the overhang in a solo session before using it in versus play, so the shape becomes something you see rather than something you construct from scratch under pressure.