Complex sentence: Koloss are of Ruin and are violent creatures that kill, with superhuman strength that grow to a maximum height of about 13 feet, at which point their hearts cannot support their bulk and they die.
Split into simpler sentences: Koloss are of Ruin and are violent creatures that kill, with superhuman strength that grow far taller than a human. This is the point at which point their hearts cannot support their bulk and they die.