During its landing, the single engine powering SN8 through the final seconds of the flight began to burn engine-rich (ingesting large amounts of copper), resulting in an unplanned lithobraking event. The engine-rich combustion was caused by low pressure in the methane header tank.

It’s not very apparent in this edit, but the green flame was incredibly bright (far brighter than normal Raptor breath, and far brighter than the sky.)