Pro Performance can be improved via Alienware Graphics Amplifier
The Alienware Graphics Amplifier is essentially an external GPU that can be used to handle graphics intensive games. It includes 350-watt PSU and 16 x PCI-E slots so most cards can fitted within it. To use it, boot the laptop with the amplifier attached.
Pro Passable performance options
Alienware 13 comes with the most powerful mobile graphics card of the previous generation, the GeForce GTX 880M. In 3DMark's Fire Strike Standard Graphics 1920x1080 benchmarks it shows a score of 6101. That's about 35% slower than 980M, the top mobile graphics card as of March, 2015.
The laptop has 2 CPU options - i5-4210U and i7-5500U with PassMark's scores of 3,437 and 4,319. As of March, 2015 the top PassMark score for a laptop CPU is just above 10,000. And while the i7-5500U is still a reasonable choice, the i5-4210U should probably be avoided.
8/16 GB of RAM.