Nice He-Man reference.
The idea that the devil is really powerful is an erroneous view. The devil is just a creature, no different than you or me. The devil isn't the evil counterpart to God, God has no counterpart. The devil doesn't have great power. On the contrary, according to orthodox Christian teaching the devil is already defeated, chained up, and waiting his final sentencing.
The devil is a liar. That's it. He lies.
In my own Lutheran tradition our most famous hymn is one written by Martin Luther himself called A Mighty Fortress, and in one of the stanzas we read "one little word shall fell him" speaking of the devil.
Lots of people have extrapolated what the "one little word" is, but Luther himself writes that the "one little word" that slays the devil is the word "liar". Call the devil a liar to his face (so to speak) and he is shown to be the impotent, powerless, underwhelming snake that he is.
Luther also joked about chasing the devil away with his farts.
So you're right, the devil is really inept.
-CryptoLutheran