Wow! A tall order! I don't know if I can fulfill all of your requests but..................
NAME ONE MUTATION that has PROVEN to be beneficial. Show me the previous version of a creature that mutated, then show me the better version that had more complexity...........You cannot use theory, either, you must use evidence.
I know of a single mutation (base pair change) in a single gene in HUMAN BEINGS that is beneficial: A "point" mutation in which valine replaces glutamate at position 6 of the hemoglobin beta-chain results in the syndrome known as SICKLE CELL ANEMIA.
The malarial parasite is an obligatory parasite for one part of it's life cycle..........it reproduces in human Red Blood Cells. The "sickling" of cells does not allow this parasite to reproduce.
A benefit of having this mutation is that IF you live in an environment that also is conducive to the malarial parasite (Africa) this mutation would be beneficial. Many people of African descent "carry" this mutation and it IS benefical for those living in Africa since they are not "easy" hosts for the malarial parasite.
I believe this fulfills all of the above challenges, except for............and became another species.