The idea I have is an atmosphere with heavy gasses so the creatures that inhabit this planet have an easier time flying.
The temperature is colder than Earth's minimum of -119°, average of 12° and maximum of 37° Celsius on the surface.
The gases I have in my mind for this atmosphere are:
3%-5% sulfur hexafluoride
10% trioxygen (between 15-25 kilometers above sea level)
0,013% carbon dioxide (three times lower than on Earth)
All my creatures lack senescence due to a fast regenerating layer that protects genetic codes like RNA, DNA, TNA, PNA, GNA and XNA, so oxidation won't be a problem, but I wonder if the world would be too flammable.
Can this support multi-cellular life capable of running, swimming, flying and gliding?
Can I somehow make flying even easier without decreasing the quality of life?