Hi,

I would like to know the difference between

riddle(n) v. Puzzle(n)

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synonyms PROBLEM, PUZZLE, ENIGMA, RIDDLE, CONUNDRUM:

PUZZLE applies to any problem notably baffling and challenging one's ingenuity or skill <there are few things in the world so difficult to explain as real change; it appears to me that most scientists are far from realising the complexity of this metaphysical puzzle -- W.R.Inge>

RIDDLE indicates a question or problem involving paradox or contradictions, often light, and usually proposed for solution as an indication of wit or intellect <I've got a brand-new riddle for you ... what's the difference between a cat and a comma? ... a comma's a pause at the end of a clause, and a cat's got claws at the end of its paws -- J.W.Ellison b.1929>

Webster's Third New International Dictionary, Unabridged.
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To remember "riddle", you could always think of Sphinx's riddle in Oedipus Rex.