If your emperor has access to wizards, I'd be tempted to use them. It doesn't matter whether you want a low-magic or high-magic campaign. In a high-magic game, his magical monuments will seem perfectly in-place. In a low-magic game, they'll be all the more impressive, and give a good sense of this guy's power and madness.
Something simple might be good. Like... floating fountains. Geysers of water erupt in mid-air, then drip down, suddenly disappearing before even a single drop hits the pavement. The emperor might place this in a smaller city to show his approval or to encourage growth. And everyone agrees that the constant, dancing fountains are very pretty to look at. Unfortunately, the magic used to create them has weakened the barriers between planes, and now water elementals and malignant fae are "slipping in" to wreak havoc.
As an alternative to the classic colleseum, how about a battle royale in the city streets? Prisonsers, young gladiators, dishonored noblemen, pesky adventurers, or anybody else who is either stupid or rebellious enough to gain the emperor's attention find themselves shackled with magical mithril neck-collars. The collars are studded with various gems worth various points, so a common criminal's amber collar might be worth only one point, while a treasonous soldier's sapphire collar might be worth five. Anyone shackled with a collar is to hunt down and kill other collared individuals until they earn enough "points" to gain their freedom. The collars contain various wards and spells to make them all but irremovable; the only way to get them off is decapitation. The king's wizard advisors scry on the contestants often, letting the emperor and his high court enjoy the show from afar.
Oh, and if anyone tries to leave the city or nation while wearing the collar, it detonates. That just goes without saying.
Something simple might be good. Like... floating fountains. Geysers of water erupt in mid-air, then drip down, suddenly disappearing before even a single drop hits the pavement. The emperor might place this in a smaller city to show his approval or to encourage growth. And everyone agrees that the constant, dancing fountains are very pretty to look at. Unfortunately, the magic used to create them has weakened the barriers between planes, and now water elementals and malignant fae are "slipping in" to wreak havoc.
As an alternative to the classic colleseum, how about a battle royale in the city streets? Prisonsers, young gladiators, dishonored noblemen, pesky adventurers, or anybody else who is either stupid or rebellious enough to gain the emperor's attention find themselves shackled with magical mithril neck-collars. The collars are studded with various gems worth various points, so a common criminal's amber collar might be worth only one point, while a treasonous soldier's sapphire collar might be worth five. Anyone shackled with a collar is to hunt down and kill other collared individuals until they earn enough "points" to gain their freedom. The collars contain various wards and spells to make them all but irremovable; the only way to get them off is decapitation. The king's wizard advisors scry on the contestants often, letting the emperor and his high court enjoy the show from afar.
Oh, and if anyone tries to leave the city or nation while wearing the collar, it detonates. That just goes without saying.