I think "Barrymore" had another actor, at least off-stage, in addition to Plummer. I remember some guy with a very nasal, funny kind of voice talking to him at some points. Plummer was wonderful. RIP.
It was indeed a two-hander, with Michael Mastro on the God mic (a role that was understudied by the production's stage manager). But Barrymore was alone onstage, which gave the illusion of a one-person show.
