Very nice art.
For the first pair, i thought of a water phoenix; one in front of a waterfall. Hope this gives some inspiration
All of them could work as a creature with hatch; they all look like a Feathered Chrysalis.
Maybe when a pair of wings for opposite elements are out they combine into one creature?
The death one (green wing; purple background) weirdly gives an illusion of a cavern; as do the aether and time ones, but a bit less.
