Sequences
Sequences are a concept created by SuperWindows78, which involves a cycling of a set of symbols or words that are used. These are similar to loops but rather then repeating previous numbers, it repeats your own set of symbols.
Like loops, each repeat makes the entry more powerful and increments the repeat counter.
These aren't often used within the community anymore, most sequences are from early-FG (???? [3] / LOE days), and we don't know why.
Mastery Sequences
Mastery Sequences are very similar to normal sequences, but instead of looping a set of symbols you loop the previous numbers. Also unlike loops, it also doesn't use a video for repeating the entries, you instead manually type in the entries and explictly state it is "mastered".
"Mastered" entries are basically overpowered versions of the respective, non-mastered variant. Some of the mastery sequences also has special effects that are applied on the number, however these has fallen out of fashion.