Very cool and tight little game loop! Immediately started to see risk-reward with fuel, expanding gameplay over time, some fun balance. I laughed hysterically the first time my own train shot or ran over me, too. Could easily see this being a fun bullethell - I wonder if you could expand this by having the trains follow routes you can place or expand the route of, having some upgrades me new rail tracks that upgrade the train temporarily as buffs when ridden over; or maybe you could hop on and off the train to get around too. Nicely done!