Patterns that aren’t exactly highlighted in the lessons or derive their meaning from their radicals.
For example, kanji that contain 月 are body parts, such as 肺(lung)、腹(stomach)、腕(arm)、脳(brain). Another example: kanji containing 复are typically read as ふく (side note: these are easy for me to remember because the mnemonic for this is f**k ). While not universal of course, these little patterns are a wonderful additional help during reviews when I can’t remember the mnemonic.
I’ve seen some of them may be mentioned as one-off in hints sometimes, but not in every entry that follows a certain pattern.