I'm looking through Howard stories and counting all the things that Gygax would have forbidden.
Let's start with Khemsa, from People of the Black Circle
This warrior, leaning on his spear, and yawning from time to time, started suddenly to his feet. He had not thought he had dozed, but a man was standing before him, a man he had not heard approach. The man wore a camel-hair robe and a green turban. In the flickering light of the cresset his features were shadowy, but a pair of lambent eyes shone surprizingly in the lurid glow.
"Who comes?" demanded the warrior, presenting his spear. "Who are you?"
The stranger did not seem perturbed, though the spear-point touched his bosom. His eyes held the warrior's with strange intensity.
"What are you obliged to do?" he asked, strangely.
"To guard the gate!" The warrior spoke thickly and mechanically; he stood rigid as a statue, his eyes slowly glazing.
"You lie! You are obliged to obey me! You have looked into my eyes, and your soul is no longer your own. Open that door!"
Stiffly, with the wooden features of an image, the guard wheeled about, drew a great key from his girdle, turned it in the massive lock and swung open the door. Then he stood at attention, his unseeing stare straight ahead of him.
A woman glided from the shadows and laid an eager hand on the mesmerist's arm.
"Bid him fetch us horses, Khemsa," she whispered.
"No need of that," answered the Rakhsha. Lifting his voice slightly he spoke to the guardsman. "I have no more use for you. Kill yourself!"
Like a man in a trance the warrior thrust the butt of his spear against the base of the wall, and placed the keen head against his body, just below the ribs. Then slowly, stolidly, he leaned against it with all his weight, so that it transfixed his body and came out between his shoulders. Sliding down the shaft he lay still, the spear jutting above him its full length, like a horrible stalk growing out of his back.
The girl stared down at him in morbid fascination, until Khemsa took her arm and led her through the gate. Torches lighted a narrow space between the outer wall and a lower inner one, in which were arched doors at regular intervals. A warrior paced this enclosure, and when the gate opened he came sauntering up, so secure in his knowledge of the prison's strength that he was not suspicious until Khemsa and the girl emerged from the archway. Then it was too late. The Rakhsha did not waste time in hypnotism, though his action savored of magic to the girl. The guard lowered his spear threateningly, opening his mouth to shout an alarm that would bring spearmen swarming out of the guardrooms at either end of the alleyway. Khemsa flicked the spear aside with his left hand, as a man might flick a straw, and his right flashed out and back, seeming gently to caress the warrior's neck in passing. And the guard pitched on his face without a sound, his head lolling on a broken neck.
Khemsa did not glance at him, but went straight to one of the arched doors and placed his open hand against the heavy bronze lock. With a rending shudder the portal buckled inward. As the girl followed him through, she saw that the thick teakwood hung in splinters, the bronze bolts were bent and twisted from their sockets, and the great hinges broken and disjointed. A thousand-pound battering-ram with forty men to swing it could have shattered the barrier no more completely. Khemsa was drunk with freedom and the exercise of his power, glorying in his might and flinging his strength about as a young giant exercises his thews with unnecessary vigor in the exultant pride of his prowess.
The broken door let them into a small courtyard, lit by a cresset. Opposite the door was a wide grille of iron bars. A hairy hand was visible, gripping one of these bars, and in the darkness behind them glimmered the whites of eyes.
Khemsa stood silent for a space, gazing into the shadows from which those glimmering eyes gave back his stare with burning intensity. Then his hand went into his robe and came out again, and from his opening fingers a shimmering feather of sparkling dust
sifted to the flags. Instantly a flare of green fire lighted the enclosure. In the brief glare the forms of seven men, standing motionless behind the bars, were limned in vivid detail; tall, hairy men in ragged hillmen's garments. They did not speak, but in their eyes blazed the fear of death, and their hairy fingers gripped the bars.
The fire died out but the glow remained, a quivering ball of lambent green that pulsed and shimmered on the flags before Khemsa's feet. The wide gaze of the tribesmen was fixed upon it. It wavered, elongated; it turned into a luminous green-smoke spiraling upward. It twisted and writhed like a great shadowy serpent, then broadened and billowed out in shining folds and whirls. It grew to a cloud moving silently over the flags--straight toward the grille. The men watched its coming with dilated eyes; the bars quivered with the grip of their desperate fingers. Bearded lips parted but no sound came forth. The green cloud rolled on the bars and blotted them from sight; like a fog it oozed through the grille and hid the men within. From the enveloping folds came a strangled gasp, as of a man plunged suddenly under the surface of water. That was all.
Khemsa touched the girl's arm, as she stood with parted lips and dilated eyes. Mechanically she turned away with him, looking back over her shoulder. Already the mist was thinning; close to the bars she saw a pair of sandalled feet, the toes turned upward--she glimpsed the indistinct outlines of seven still, prostrate shapes.
"And now for a steed swifter than the fastest horse ever bred in a mortal stable," Khemsa was saying. "We will be in Afghulistan before dawn."
Now imagine that Howard was trying to get Khemsa accepted as a magic-user in Gygax's campaign:
Howard: Okay, Khemsa sneaks up on the guard...
Gygax: Nope, sneaking is for thieves unless you have a special cloak of invisibility.
Howard: And Khemsa hypnotizes the guard to kill himself!
Gygax: Nope, that's a self-destructive command, that's forbidden in my rule-book.
Howard: Then he parries a spear bare-handed and breaks a guy's neck.
Gygax: No way. He's not some kind of martial artist, he's a scrawny bookworm.
Howard: Then he puts his hand on a thick door and smashes it.
Gygax: Not going to happen. That's a job for a warrior. Even a knock spell would just unlock it.
Howard: You don't get it. Khemsa is powerful. He exults in exercising his power.
Gygax: No, he's locked into spells that work just one way, and he runs out of ammo quickly.
Howard: Then he uses powder to summon a silent, slithering smoke to suffocate some captives.
Gygax: Okay, but he uses up material components and gets no experience points.
Howard: Then he summons a mount faster than any mortal horse.
Gygax: No way, he gets one standard warhorse or two riding horses, your choice.
Howard's wizards never had to deal with player envy, or campaign balance. Howard's wizards and magic items were able to do whatever was necessary for the plot to progress, and no one could play-test through the stories to prove inconsistencies.
Arneson imposed a lot of arbitrary limits just to invent a fantasy wargame, and Gygax imposed a lot more limits. They deserve credit for making a workable game. But by the time the two of them were done, the result was not very much like anything in Appendix N.