×As adS had said, there are 24 enclosed corner and 13 decoy potion. And as blorx mentioned in the H&S thread for 4W, cutting mud removes 1 enclosed corner and cutting tar removes 2 enclosed corner (assuming no double-stab), so we need to cut 2 mud pieces, then all tar.
Double-stab is bad because double-stab removes less enclosed corners than optimal. If we don't remove enough enclosed corners, obviously some tar will be left there.
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×Because we don't want to double-stab, for a cuttable piece of tar blob, every decoy's sword must cover a
distinct connecting pair of enclosed corner. Then when the blob turns into tar, since every pair of enclosed corner is sworded, they must break down. No tarstuff cascade trickery is involved because there is no double-stabbing happening at all.
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×Hence, basically you just need to: find the domino tiling for your configuration of blob; and then place the decoys so their swords hit exactly the center of these dominos.
Once you get this mindset going, these kinds of rooms are pretty easy.
