Exodus 8

"But the magicians did the same things by their secret arts; they also made frogs come up on the land of Egypt. Pharaoh summoned Moses and Aaron and said, “Pray to the Lord to take the frogs away from me and my people, and I will let your people go to offer sacrifices to the Lord.”..but when the magicians tried to produce gnats by their secret arts, they could not." vv.7-8,18 

Read chapter 8
How these machines were able to bring all these frogs we don't know, but it hardly helped and actually made it worse with even more page of frogs. The Pharaoh dissent even call on the magicians to stop this plague and make the frogs die or leave but he calls on Moses and Aaron. He asks them to intercede to God for him and all Egypt realizing there's something different about this God than all their gods. The next plague of lice the magicians are not able to perform likewise. God allowed them to be able to mimic the first couple of miracles but not another to show their limits and God's unlimitedness. God can do so much more than we can imagine. No one is like our God. Theres' no formula to His miracles . The magicians finally give in and finally attribute God as God in verse 19. Some people say if only they'd see God do a miracle they'd believe, yet it took many outward miracles for these magicians to believe and even more for Pharaoh and eve by the end of his life didn't honor God as the Only God. So what does tit take for you to believe with our without miracles? In what ways are you limiting God in His power?