Writing fantasy fiction is walking a tightrope. On the one hand, if you use too many fantasy clichés - words like "eldritch", "etherial"; characters like pointy-eared elves and gruff, grumpy dwarfs - you're in danger of annoying readers whose tastes run to other genres, not to mention boring readers who read only fantasy, and, which is more, failing to stand out from the fanfic crowd.
On the other hand, slavishly avoid all the clichés, and you will either alienate most of your target audience, or find yourself searching the thesaurus for alternatives and grossly inflating your text with descriptions.
Cliché is good, in moderation. Think of the trouble you'd have describing your main character when he is casting a spell if you can't use the word "glow". Whether "eldritch", "other-worldly" (which is the literal meaning of eldritch, btw), mysterious, supernatural, eerie, wierd, queer (can't really use that one any more), casting magic is almost always associated with a glow of some sort. If you want to avoid this cliché, you have to come up with a new and refreshing way of indicating that someone is doing magic. It's been tried, with varying degrees of success.
The problem is that unless your story pivots on this different kind of magic, you'll spend and awful lot of time describing how it works, and not advancing the plot.
The Cliché is Often Right
Eldritch, as I mention above, means "from elsewhere". Usually this is used to mean "beyond the grave". It's wrong to use it if all you mean is "creepy" or "scary". It's right and proper to use it if you mean "other-worldly" or "from beyond the grave" AND creepy and scary.
Unnatural is often a much more unsettling word than "supernatural". Supernatural is now so over used that it is almost impossible to say it with a straight face. Indeed, many readers take it to be the author saying: "use your imagination, I can't be bothered to". Hiding it behind near-similes like "preternatural" or "eldritch" just looks cheap, or plain wrong. Theres a significant difference of denotation between super- and preter- natural. Supernatural denotes "above or beyond the natural". Preternatural denotes "more than is usually natural". There need be no magic behind it at all, although there can. If Herman the Hero is the greatest swordsman in the known world, then his skill is preternatural. If his arch enemy, Dave the Dark Lord gets his amazing skill with a Poleaxe from the Amulet of Totally Amazing Skill with a Poleaxe, then his skill is supernatural.
Use the cliché words with precision, and they cease to be jarring and irritating. Don't be afraid to use them repeatedly if they mean exactly what you want them to mean.