The Abominable Dr. Phibes (1971), directed by Robert Fuest.
Dr Anton Phibes (PhD Theology, Heidelberg, and noted theater organist) may have had his face burned off and can speak only through a tube, but that will not stop him from exacting revenge on the doctors who could not save his wife. His means: cleverly sadistic murders inspired by the Plagues of Egypt.
This horror-comedy is a remarkably odd little film, a 1920s art deco piece proleptically informed by 1960s mod art motifs and crooner music. The visual composition sometimes rises above B-movie needs and becomes quite fine.
Despite the appealing weirdness, I prefer Theater of Blood (1973), a similar comedy revenge story Price made with Diana Rigg a couple of years later.
Oddities:
Phibes also has a young, pretty, mute assistant, but no explanation of who she is or how she comes to be with him.
We have no reason to think the doomed doctors were negligent, but Phibes is deranged by his love for his dead wife, making this a horror-romance. Actually, that's a continuing theme in Price's horror films.
One of the murders has a man impaled on a brass unicorn's head which we are told was fired from a catapult. I don't know which plague that was supposed to be.
Available on Blu-ray with an unexpectedly good image. Two commentary tracks: a low energy (and very faint) conversation with the director, and a gushing appreciation by a serious fan.