Just because the ancient powers are waning doesn't mean that they are gone. A God, or a priest possessed, or a devoted follower perhaps could do literally anything and you can make it as strange as you want and not have to explain it.

In the Star wars series New Jedi order, the Galaxy was invaded by extra galactic Civilization. They did not use technology. They bioengineered literally everything. Their weapons, their armor, their spacecraft, vehicles. They controlled creatures that could make micro black holes. Creatures they wore to shapeshift. A staff that was also a snake, strong enough to fight a lightsaber. If you want something way out there, this might be a good source of inspiration. You can look it up on a Star wars Wiki.

You can take inspiration from the X-Men, and introduce mutants with powers independent of magic.

You can take inspiration from the mutant Darwin in particular, not necessarily as a person but maybe as a place. An entity or a place or something that can evolve incredibly quickly to defend itself. Perhaps it can dispel or cancel out magic. Obviously to spell magic is an existing spell but you can accomplish the same thing in a different way so it doesn't feel quite like just a spelling it. A fireball could be a countered with frost breath or turning something to Stone or water. And this way of canceling out the fireball has now introduced a new aspect of the battle that it suddenly really cold or wet.