Create a new empty rack (File > New) and add the following devices from the "Create" menu in order: Mixer 14:2, NN-XT Advanced Sampler, Scream 4 Distortion.
Click on the "Browse Patch" button on the NN-XT and load the following sample: Reason Factory Sound Bank > NN-XT Sampler Patches > Guitar and Plucked > Ac Dark Steel.sxt
Select the "EasyFuzz" patch on the Scream 4 Distortion processor (if it is not the default) and set the Damage Type to "Scream."
Play your MIDI controller while adjusting the P1, P2 and Damage Control settings to your liking.
Save your project so you don't lose the settings you just dialed in.
Experiment with different guitar samples on the NN-XT, as well as different patches and settings on the Scream 4 Distortion processor. You will surely find many different combinations that provide a good metal guitar sound.