Complex sentence: Markus is an expert swordsman, having had centuries to master the weapon, it is believed that Markus has lost what little vulnerability he had left to the sun, although he may not possess his full strength in direct sunlight.
Split into simpler sentences: Markus is an expert swordsman, having had centuries to master the weapon. It is believed that Markus has lost what little vulnerability he had left to the sun, although he may not possess his full strength in direct sunlight.