reports that a voice over casting call has revealed some potentially major Portal 2 details. The casting call was discovered by a tipster on breakdownexpress.com, a website devoted to listing casting calls for various projects. The casting call, which requires a subscription to view), is for a major role in the sequel, described as someone who "Goes from sidekick to principal antagonist." We won't spoil more than that here. Those who aren't worried about spoilers can find more info after the break.