I haven’t yet found any threads that do hard discussion of game mechanics, so maybe this would be something beneficial to begin and once we have enough information collected we could put together a guide for stickying? Or it could be added to one of the existing FAQs
If someone has a thread already with this information, I have missed it, so please feel free to slap me and point me in the right direction.
Starting things off, I’ve observed a number of different permutations of combos that result in Critical tiles (especially useful for characters like Cap and Mags who are able to effect targeted tile changes), several of them were a bit of a surprise, so it is possible that not everyone knows all of them. Any of these work as is or if rotated 90°, 180°, or 270°. I don’t have screenshots, but you are more than welcome to test them for yourself!
Rectangle
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Shifted Rectangle
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Deep Shifted Rectangle
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Plus sign
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T
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L
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Bar
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I believe that all the others I’ve encountered are built on one of these 7 basic forms. From these 7 it seems that we can generalize the combo as two matches that may be connected by a shared tile or may run parallel and adjacent to one another. It is important to note that combinations beyond these (such as an H shape which involves 3 linked matches) will not provide additional critical tiles, so if you want to produce more than one critical tile, you’ll need to create two of the above, but without linking them.
If you have a suggestion about better (or older?) names or how to better graphically represent these combinations I am all ears.
EDIT: updated characteristics per Cousin Simpson’s recommendation, and added Blue Shoe’s point about multi-combos