A lot. For starters, the GR Corolla comes standard with an all-wheel-drive system to best help putting those 300 ponies to work. Plus, it's adjustable. The driver can adjust the AWD system to send 40%, 50% or 70% of its power to the rear wheels. The short-throw manual transmission comes with automatic rev matching to facilitate supersmooth downshifts. Front and rear limited-slip differentials are also available, and they enhance the GR Corolla's traction when powering out of corners even further. This hot hatch is a rally driver's dream.
To stiffen up the Corolla's body structure for GR duty, Toyota added underfloor bracing, additional weld points and more structural adhesive in key areas. The stiffer structure allowed Toyota's engineers to further dial in the car's suspension for responsive and accurate handling. (The Morizo Edition gets even more bracing and structural adhesive compared to the Core and Circuit Edition.)
But wait, there's more. The Circuit Edition and Morizo Edition get a roof made of forged carbon fiber to shave weight and reduce the car's center of gravity. Typically, a carbon-fiber roof is something reserved for a performance coupe like a BMW M4, not a workaday Toyota.
Incidentally, the Morizo Edition name has a bit of a backstory. Back in 2007, Akio Toyoda (then vice president of Toyota, now the president) wanted to branch out into more racing and to use the endeavor to hone the development of the automaker's cars. The effort wasn't officially approved by the company at the time, so a number of employees, including Akio Toyoda himself, went racing at the famous 24 Hours of Nürburgring endurance race.
Toyoda had received some criticism for the move, with some believing it was too dangerous for someone in his position. He decided to race under the name Morizo, kicking off an interesting era in which his true identity was neither confirmed nor denied by Toyota's media relations team.