Complex sentence: At the same time, Ryan was cast in comedy series "Sing It!" as Holli Holiday, a famous and egocentric singer, who uses the fictional talent show "Sing It!" to self-promote.
Split into simpler sentences: At the same time, Ryan was confirmed in the cast of comedy series "Sing It!". Ryan played Holli Holiday, a famous and egocentric singer, who uses the fictional talent show "Sing It!" to self-promote.