Moses encountered this with the plagues. The priests could match many of his acts so the proof escalated.
That’s right - thanks. And again, it was control of nature that the priests couldn’t match - Nile turning red, locusts, frogs, boils, etc. My pastor mentioned when Elijah (?) brought down the lightening on the pile of water-soaked wood as one other rare example. (Oh, and that whole parting of the sea thing Moses did!)