Double Top
Two peaks at approximately the same level separated by a trough, completing when price closes below that trough.
The simplest failure-to-advance shape: price reaches a level, retreats, returns to the same level and cannot pass it. Its weakness as a signal is that "approximately the same level" is doing a great deal of work — two peaks within a few percent of each other appear in almost any series if you look at enough bars. The detector requires the peaks to be closer together than the recent average range and separated by a trough deep enough that the two are genuinely distinct attempts rather than one choppy top.