Under The Stones Sacrifice Shape List

Three plus one  

If the three stones are captured, the one lonely stone can cause a shortage of liberties, which allows under the stones. Example: https://www.goproblems.com/problems/438

Bent Three  

Though very rare compared to other shapes, but it exists. An example is Under The Stones Problem 8.

Bent Four with a cutting point  

After cutting by Black, a ko fight for life occurs. https://www.goproblems.com/problems/4907

It is a Twisted Four...

Empty triangle oiotoshi  

Also, a captured empty triangle can cause an under-the-stones-ish capture, but for it to work, black must remove an outside liberty after white captures. This can, however, lead to interesting connection tesujis:

Black can connect even if white captures the 3 stones.

DrStraw: Better for B to play back into the center of the 3 stones than to fill an outside liberty. The effect on B'S shape is the same, but W is not as good.

Shapes that can lead to aforementioned ones:

unkx80: Making a more general statement, I believe the sacrifice stones may be the following shapes, with the optional addition of stones in the x direction or beyond.

Bent three in the corner  

Black picks up 0.5 point.

OC, if we are going to include shapes where the question is points, there is no end. E. g., bent seventeen.

Bent seventeen (ii)  

at .

This is a 2/3 point Black sente (unless White is komaster, when it is worth 1 2/3 points).

Charles The one time it actually happened to me ...

Example  

... was when I made the mistake of playing here, thinking it was a snapback .