“They” are called Catholics, and they do it every Sunday.
Not without the 12V. I’m pretty sure most of the internal electronics are dependent on that working. There’s an access port so you can “jump” the 12V with another car, which I think would then allow you to open the door though.
You can also “jump” the car to open it via a 12V access port in the front.
Cassette Beasts might work. Turn based, collect monsters for new powers, and local co-op!
I just bought the skyconnect. It will also support Thread soon!
If you’re sticking with Marlin, I’ve been very happy with the “professional” firmware. The configurator is pretty easy to set up if you change any hardware like a new bltouch or new hotend if that’s your thing.