Complex sentence: During his stay in Frankenstein Castle he practiced alchemy and anatomy.During his stay he created an an animal oil known as Dippel's Oil which was supposed to be the equivalent to the Elixer of Life.
Split into simpler sentences: During his stay in Frankenstein Castle he practiced alchemy and anatomy. While at Frankenstein Castle he created an an animal oil known as Dippel's Oil which was supposed to be the equivalent to the Elixer of Life.