Complex sentence: Fichtner, attracted to the potential of the character, was cast as Mahone just one day before filming began for the second season; he signed on for only two seasons, but was convinced to appear in a third.
Split into simpler sentences: Fichtner, attracted to the potential of the character, was cast as Mahone just one day before filming began for the second season. Fichtner signed on for only two seasons, but was convinced to appear in a third.