It all about special editions and exclusive models lately, as automakers try to go the extra mile by packing more equipment and visual upgrades on their standard models. 
This is also the case with the Mercedes C Class DR 520 for which production will be limited to only 20 units and which is based on the C 63 AMG.
The Mercedes C 63 AMG DR 520 comes with increased performance as it unleashes 520 HP and 650 Nm of torque, (60 HP and 50 Nm more than the regular version), so accelerating from 0 to 100 Km/h is now taking 4.1 seconds in the saloon and 4.2 seconds in the Estate, while both have a limited top speed of 187 mph.
The extra power comes due to the fact that the Mercedes C 63 AMG DR 520 features forged pistons, new connection rods and a revised crankshaft, and the new high-performance braking system will provide the stoppage force required.
On the visual side the Mercedes C 63 AMG DR 520 come with a black or white matt wrapp, Titanium finish alloys and grille, the DR 520 badging plus sports seats, a multi-function AMG steering wheel and Nappa leather and Alcantara at the interior. 
The Mercedes C 63 AMG DR 520 price is 62,430 GBP for the Saloon while the Estate goes on sale priced at 63,680 GBP.
Mercedes press release :
Mercedes-Benz UK has launched an exclusive new model, the C-Class DR
520 with more power and performance than any other C-Class.  Only 20
units of this car will be available, and it is sold exclusively through
the company’s Specialist Products division at Mercedes-Benz World at
Brooklands, Surrey.
Based on the high-performance C 63 AMG, the DR 520 has a performance
upgrade and boasts 520 hp and 650 Nm of torque, a 60 hp and 50 Nm
advantage over than the standard C 63 AMG.  The DR 520 Saloon can reach
0-62 mph in just 4.1 seconds with the Estate achieving the same in 4.2
seconds, and both are electronically limited to a top speed of 187 mph.
The AMG Performance Pack Plus is fitted to the DR 520 as standard and
features AMG’s high-performance braking system with red calipers, with
the addition of engine upgrades in the form of forged pistons,
newly-developed connecting rods and a revised crankshaft, as well as an
AMG Carbon Fibre rear spoiler for the Saloon.
Available with a black or white matt wrap and complimented by
Titanium finish alloy wheels, grille and discreet DR 520 badging on the
wing and the boot lid, the DR 520 combines stealthy looks with potent
Inside, the sports seats are upholstered in leather and exclusive
Alcantara finished with red or white contrast stitching, as is the
dashboard and upper door panels.  The multi-function AMG Performance
steering wheel is clad in Nappa leather and Alcantara.
Nigel Unsworth, Specialist Products Division Manager commented:  “We
wanted to launch the Specialist Products Division with something unique –
and the DR 520 fits the bill perfectly.  Mercedes-Benz World is located
at Brooklands, and there’s a proud history of ‘Brooklands Specials’
being sold here over the years.  The DR 520 – which is dyno-rated at 520
hp – is our chance to create an exclusive model in the UK.  It’s a
great opportunity for us to offer our customers who enjoy sports and
supercars a bespoke car with even more performance than the already very
successful C 63 AMG.  And as well as the increased performance, it
looks incredible, too.”
The DR 520 costs £9,995 above the standard C 63 AMG price, making the
DR 520 Saloon £62,430 OTR and the Estate £63,680 OTR.  The cars are
also backed by a three-year, 60,000 mileage warranty.

Source: Mercedes