My suggestion would be to not get too hung up on the art. A simple drawing of one of your characters or mythical beasts would suffice.
It brings to mind a book I read years ago, called The Chrysalids. It’s a very popular YA book (it is assigned reading in many schools, or at least it was 40 years ago). It’s about a group of telepathic kids living in a post-apocalyptic world where religion is supreme and any little birth defect of difference is considered a blasphemy that must be destroyed. Naturally, telepathy would be considered a blasphemy.
At one point in the story it is revealed that a character has six toes, and she is found out when somebody sees her wet footprint, hence this simple cover:

There was also another cover, equally simple, showing the characters doing their telepathy thing:

Neither are artistic masterpieces, but they both reveal something of the plot.