Demolition Derby turns your carriage into a battering ram that takes less punishment. It is a level 6 skill costing six points.
Demolition Derby sits at position 18 of 18 in the Ecosystem tree. Unlocking Demolition Derby takes 6 skill points. You need level 6 before you can buy it. Jacob and Evie each have their own skill tree, so you buy Demolition Derby once for each twin.