Fantastic Science: Koura may be a user of this. While he clearly uses Black Magic (like animating the figurehead on Sinbad's ship), he also seems to use a form of chemical explosive to trap Sinbad in the cave on Lemuria.
It was actually Baker's stunning performance as Koura that brought him to the attention of the Doctor Who producers when they set out to find a new Doctor to replace Jon Pertwee.
Too Dumb to Live: YMMV on this, but Sinbad and his crew trying to sword-fight Kali, a statue made of stone (or metal, it's hard to tell). There is no way that swords could hurt it, and they have to knock it off a ledge to break it, anyway. Why not try to run or draw it out of the enclosed temple?
Took the Bad Film Seriously: Everyone is well aware they're in a fantasy film Starring Special Effects and play their roles with copious Dull Surprise and Parent Service. Except for Tom Baker as Koura, who goes out of his way to play his generic evil wizard as a Shakespearean Tragic Hero with an inner world, going along with the Fridge Horror (that the character is probably a teenager who merely appears older due to his Cast from Lifespan magic powers) and going against the script in places to make his character come across as noble and fascinating rather than the Card-Carrying Villain he was written as. He's a strong enough character that when he finally accomplishes his evil plan at the end and has to be killed, it's actually upsetting because of how sympathetic he was. He even ramps up the sexuality to upstage all of the pretty people without shirts that he's cast against, moaning magic prayers orgasmically and smouldering. Since it was this role that the producers of the BBC saw him in to check he could act before casting him in that role he defined, it is probably for the best.
Uncanny Valley: The centaur's all-too-human screams unnerved some viewers.