It’s a question worth asking, and the answer is “whatever he can”. He will press your defenses until he finds a weakness. That’s why Paul tells the Ephesians to suit up and put their big boy armor on. If the Ephesians walk in love, walk in the light, and walk in everything else that Paul told them in his letter, so that they radiate the light of God’s glory like the temple, then rest assured, the army of darkness will come to plunder it in response.
Therefore, he tells them to make their “stand”. The term stand is repeated 7 times in that short passage. He’s telling them to dig in. The enemy is coming in for a blow, and they don’t have the required strength, prowess, or skill to stop him. Like Rocky Balboa, they just need to stand their and take the beating until the bell dings. Sometimes standing is all you need to make you a champion, so that you can shout speckles of spit through your swollen face, “Yo Jesus…I did it!!!” But you’re not alone. In fact, Paul terms standing in that armor as standing in “the armor of God” and rephrases it as “the power of HIS might”…