A unique take is preferred or something similar to the Japanese original. The first and last form aren't required to have separate voices however there should be noticeably different traits and speaking patterns between the two.

Cell is a bio-android created by Dr. Gero/Android 20. He is comprised of cells taken from Earth's mightiest warriors including that of Goku, Piccolo, Vegeta and many others. In his first form he preys on humans to increase his power, however, Cell ultimately requires Androids 17 & 18 to complete his 3 stage evolution.