S4·E13 Christmas Special: Scrapheap Mega Challenge: All-Terrain Marathon

The mega challenge is to build a hybrid machine to face a two-day triathlon. Stage one is flat out on the salt-flats. Stage two is in a canyon littered with giant boulders. And stage three is on a lake: yes, we're talking amphibious vehicles. The winner of each stage collects three points, the runner-up two and the third-placed team one. The team with the most points at the end of the third stage will be the mega champions.