Tutorial Videos

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The Basics

Grim Grotto is a prophecy method. It is an S or Z skim that creates a T-spin triple or C-spin. It has many variants.

This is the standard variant that creates a T-spin triple:

Diagram Set 29-1
1	2

Create or spot this L-shaped mid-game opportunity in a 3-wide gap.

Skim using a horizontal Z. Add an overhang. You get a T-spin triple.

Variations

Grim Grotto has several variations. One sub-variation, Crush, is classified here because of its conceptual similarity.

1. Greedier Grim Grotto

There is a greedier version of Grim Grotto to create a C-spin:

Diagram Set 29-2
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Spot this 3-wide gap mid-game pattern. Insert a vertical Z into it.

Add an L and overhang. You get a C-spin setup.

2. Crush

The method below is called Crush. It helps to create T-spin triples or C-spins:

Diagram Set 29-3
1

Alt. A

Alt. B

The player skims with LZ or JS to transform the first step into a C-spin.

Here are other sub-variations of Crush:

Diagram Set 29-4
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The player skims with a J to make a prophecy T-spin double.

You can also create it in a 3-wide gap situation:

Diagram Set 29-5
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Spot a 3-wide gap and place a horizontal Z piece into it.

Skim it with an L piece and make an overhang for a T-spin triple.

The below B is helpful as an STSD alternative. Both share the same starting 3-wide-well condition:

Diagram Set 29-6
A	B

Crush shares the same 3-wide mid-game opportunity as an STSD, letting you make a prophecy C-spin from the same condition.

3. Crush (Garbage Version)

Crush has a practical mid-game situation when garbage is overlapping, as shown in step 1 below:

Diagram Set 29-7
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Spot this common mid-game overlapping garbage pattern.

With a simple L-skim and an overhang, you get a quick T-spin triple.

This method is commonly used by high-level players, such as Doremy.

Advanced

Crush has advanced variations.

1. Stacking Crushes

You can also do this if the 3-wide well height is too high to make an overhang for an STSD:

Diagram Set 29-8
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This 3-wide well is too high to make an overhang for an STSD.

The player tops the J part with a J and S to skim. He tops an overhang with Z.

3

The resultant pattern makes a T-spin triple above the bottom STSD. This is essentially a King Crimson with 3 T-spins.

Crush is thus a suitable method if your corners are too highly stacked for an STSD overhang.

In a Nutshell

Grim Grottos provide many ways to create mid-game T-spin triples and C-spins. They are among the most practical and flexible prophecy T-spin setups.

Very strangely, I do not observe enough high-level players using them.

Pros and Cons
Pros	Provides additional ways to create T-spins. Crush can be used to fix overly tall STSDs. Crush can be used in common garbage hole patterns.
Cons	Breaks back-to-back bonuses and incurs a line clear delay.