Have been planning on using some of those Infernal War Machines from Avernus in my campaign. Been playing a very modified version of Red Hand of Doom, group is currently heading back to town after seeing a massive hobgoblin army. They're gonna take a long rest after getting torn up by a young dragon, and will have a rude awakening to two riders passing through. Decided to change up how they're fueled instead of using a soul coin. Never felt like the soul coins really served their purpose of making a player hesitant to expend a soul and feel bad about it. Instead you must fuel the machine by putting a living victim inside the large pod in the from. When they open it it will be covered with markings of like magic runes and burnt up gore. Hobgoblin army fuels their bikes with spare goblins, but are heading to town for fuel with a purer soul. The purer the soul the longer it runs.