For a max difficulty run, you need plenty of combustibles to lob against fog. Use this blueprint with a coal miner close to fog to eradicate them within 15 minutes playtime. After destroying their bases: keep destroying them (when they have almost built the core fully), or alternatively use the geothermal blueprint exploit.

Produces: 1.5/s combustible units
Consumes: 4.5/s coal
Power: 1.62 MW