If you have under 30 Dex as the Necromancer (and, probably, any class), you won't be able to hit anything on the second floor.
Now when you read that, you may think I mean: "You will hit things LESS OFTEN", but no, I don't.
You will not be able to hit anything. Not a single attack will resolve.
As the developer's funny little joke, despite having 42 Armor, nothing will have trouble hitting *you*.
Since you cannot ascend after falling down a floor; plan accordingly, otherwise it will softlock your run, which is far more frustrating on Nethack than it ought to be.