A lot of metal features down-tuning. Regular tuning is E-E which is fine for some metal players, however, some like to tune one, or all six of their strings lower. A slightly longer scale length can help with tuning stability if you’re tuning way down to around C or B. Baritone guitars can be a good option as they have a much longer scale length – usually around 27”, and have a regular tuning of B-B.
Some of the best metal guitars have more strings. 7 and even 8-string guitars provide a much wider frequency range. You’ve still got the high end with your top strings, allowing you more space to solo but when you need that earth-shattering low end, you’ve got it at your disposal with an additional low string.