Sheen says it's time for his character to start "circling the drain"
The FX star allegedly demanded Blair be fired because he believed she'd been bad-mouthing him
Selma Blair, Joshua Close, James D'Arcy and Rachel Miner star in the Canadian psychological thriller
Blair and Smith will play Sheen's therapist and ex-wife, respectively
The "Boardwalk Empire" star will make a guest appearance on Fred Armisen's upcoming HBO series