What element is this? What can it be used for?
It's a new part for 2021, and as the name implies, one of it's main uses is as a leg on various creatures. It seems especially well-suited for building spiders:
It hasn't had many other official uses to date, but it does get used as a robot of some kind in the Marvel advent calendar:
Stylistically, the part is very similar to 11090 Bar Holder with Clip
It's easy to imagine how bars could be used to integrate these parts together into larger structures.
In terms of size, the part is 2 modules in its longer dimension, and 1.5 modules in its shorter dimension:
There are of course many, many ways this piece could be used, but one that came to my mind was using it as part of wrought iron stair rail design. This works nicely, but we do have to use stairs with a tread depth of 1.5 modules to allow the railings to touch:
This part adds new flexibility to the bar and clip family, and I'm excited to see it get used more in the future.