a left-arrow anchor, or running men pattern.
An anchor (also known as running men) is a variation on stream, where there's 1 recurring arrow that you need to keep hitting every other note. The other notes are alternating between 2 or 3 notes, if it's only alternating with 1 other note, it's considered a trill. The best way to explain this pattern is through the example gif. Anchors are one of the most difficult pattern to master.
Crossovers. Can also be considered up-arrow and down-arrow anchors.
A crossover is a variation of an anchor. In crossovers, the anchor is on either the down or up arrow and follows the pattern in the example gif. It's called a crossover because if you were attempting this on a dance pad, you would need to cross one foot over the other to hit it correctly.