I just want to slowly watch the flames burn over the enemy planet. What weapon could do that. Just "scorched earth" a planet
Plasma Bombardment Halo Style does that pretty well, especially if you just lob the plasma at the atmosphere instead of directly on the surface. Sure in Halo they glass the planet, but that is only the end result, on the border between glassed and non-glassed parts of the area, there are massive firestorms. So if you take a less intensive approach then the Covenant does, you can set the entire planet on fire and boil off the oceans, for quite a extensive period of time before you run into issues like burning off to much of the atmosphere. (i.e. after a while, the entire atmosphere becomes hotter then the ignition temperature of oxidizable shit on the surface, long before you reach temperatures that would melt the surface.)
Probably more economic way of doing it compared to conventional methods like firebombing/napalm/thermobaric weapons.
