A proper 4WD system, LSD or lockable diff in the rear, and a turbodiesel.
Do it, 'yota. You have an amazing off-roading heritage to live up to, and you would make a killing stateside.
In fact, they already offer the Auris with a 2.2TD (2AD-FHV) that pumps out 177hp and 300lb.ft. Take that, throw 4WD on it with a rear locker, you've got a hit.