Each plague was a direct attack on the related Egyptian deities.
For instance:
The turning of water to blood (NOT just the Nile water, but every vessel or puddle in the area!) was a direct attack on the Nile itself, which the Egyptians worshipped as their source of life. This plague confronted the various river deities, including Khnum, Hapi, and Osiris (his blood was supposed to be the Nile itself). By turning the water to blood and killing the fish (supposedly protected by Hathor and Neith), Moses was not only shaming all these Egyptian objects of worship, but also showed that sustenance comes only from the hand of Yahweh.
Plague #2-- the invasion of the frogs--was an attack on the goddess Heqet (sometimes depicted with a frog's head), as well as Isis. Frogs were sacred to the Egyptians. However, these goddesses were powerless to prevent these symbols of life from becoming rotting piles of death.
It is of interest to note that the Egyptian sorcerers mimicked the plagues of blood and frogs with their enchantments. While they possibly could have been mere simulations (illusions), it is more likely that demonic power was involved. However, God allowed them to add to these plagues using their demonic powers, but NOT to reverse them!
Plague #3 (invasion of the annoying insects other than flies from the dust of the earth) confronted all the gods of the earth (i.e. Akhor). This and plague #4 (flies) confronted the Scarab beetle "god" Khepri. A plague of flies shows that this "god" was not doing his job (burying dung, which makes it inaccessible to flies for breeding in).
Plague #5, death of the livestock (source of food, milk, clothing, transportation) was a direct assault on the sacred Apis bull; and Mnevis, a bull-god symbol of fertility; and Hathor (again, because of her representation as a cow), as well as Isis (again) who wore a cow's horns on her head. They were all shown to be imposters.
Plague #6, the boils, showed the impotence of any of the gods of magic and healing, such as Hike and Thoth, to protect even the magicians from the boils and thus showed them impotent against the power of Yahweh.
Plague #7, hail, and #8, locusts (brought by the WIND), that destroyed the crops, attacked the various sky deities (i.e. Shu, Tefnut, and Nut, deities of air, moisture, and sky) who supposedly controlled the weather. The loss of the crops showed the impotence of the gods of vegetation and agriculture (e.g. Geb and Seth).
The 9the plague, darkness, was an attack on the supreme deity of Egypt, the sun-god Ra, who was believed to bring light and heat to the earth. Otehr sky gods rendered impotent were Horus, Seker, Khepri, Mut, and Nut.
Finally, plague #10, death of the firstborn, was an attack on the divinity of Pharaoh himself, whom the Egyptians believed was an incarnation of the sun-god and of Osiris, the giver of life. It was the Pharaoh's task to retain the favor of the gods and to uphold the laws of Ma'at, goddess of order. However, he was powerless to prevent the death of his own son, the next-in-line "divine ruler", or that of anyone else's son in the land of Egypt. Thus, Yahweh ALONE had absolute control over life and death.
If God actually did showdowns like this today (also like the God vs. Baal showdown with Elijah presiding), there would be absolutely no doubt which 'religion' is 'right'.
