Perfect rhymes:
* Bismal (archaic word meaning "vile" or "unpleasant")
* Chismal (a rare word meaning "a small piece")
* Frismal (a rare word meaning "a small, brittle piece")
Near rhymes:
* Abysmal
* Prismal
* Risible (meaning "laughable")
Eye rhymes (words that look like they rhyme, but don't):
* Dismal (this is the word itself)
* Formal
Choosing the best rhyming word depends on the context and desired effect.