It was most likely an archangel or leader of angels of some kind. Some have imagined anglelic hierarchies with the seraphim as the highest ranked angels, so it is possible.
At least that demonstrates that angels can be serpent-like.
Not to me. The Bible says angels are nonphysical beings which very much sound like they are created by design. Aliens would be physical like us and a product of evolution somewhere else. I am more likely to compare angels with robots and artificial intelligence than aliens – only of a spiritual substance rather than physical. Spiritual simply meaning things which are not part of the mathematical space-time structure of the physical universe.
I don’t believe in magic, but I do believe in a non-physical dimension to existence. God is non-physical after all. And for me the existence of a non-physical aspect to existence is a big part of why I would even believe in any of the religious stuff. To me the physical looks artificial and contrived to me and I find it hard to believe that this is the limit of reality.
It is easy for me to imagine God creating angels as a first step in the more straight forward way of creating spiritual beings like Himself by design giving them whatever knowledge and abilities He chose. But they would largely be more like tools and extensions of Himself (so the Bible describes them as servants). Not being satisfied with this shows that God sought more of an authentic relationship with beings apart from Himself – beings who create themselves by their own choices, growth, and learning.