Complex sentence: Blackwolf declares his magic superior to Avatar's and demands his surrender; whereupon Avatar offers to show Blackwolf a trick he learned from their mother; then pulls a pistol from his sleeve and kills Blackwolf.
Split into simpler sentences: Blackwolf declares his magic superior to Avatar's and demands his surrender; whereupon Avatar offers to show Blackwolf a trick he learned from their mother. Avatar then pulls a pistol from his sleeve and kills Blackwolf.