Recently I have been fiddling with "cars" of minecarts. To make the "train" I had you need to make a few of these cars by compressing a ton of minecarts together, then smashing them into eachother on a rail. You it run with you at the front as it goes off the rail, and about 100 blocks away stick a sideways off powered rail with a block behind it. As it rams into the pair, it twists sideways and falls through the ground. In one of the snapshots in the zip folder, you may see a hole from me digging up the first time. You will also see a minecart half in the ground, as well as me doing things in the carts and the track setup.

I FORGOT TO MENTION THIS IS IN FACT IN VANILLA. The cars and trains are made by minecart friction bugs.(are they?)