Okay, I thought about some rules for this
For start:
Each player takes three emperors from their deck, and puts them into play (choose one to be the current reigning emperor and the others to be senatorial). Then draws 4 cards from the deck.
Emperors have these stats:
Strenght: Matters when fighting against other emperors
Stamina: How many blows can the emperor take
Speed: During the combat phase, the emperor with higher speed attacks first, and Every card has a speed value. You cannot play cards in one turn that would have combined speed higher than your emperors. For ex. Gladius has speed 2 Fountains have speed 3 and your emperor has speed 3. You can only play one card right now. But the other will have to wait for the next turn
Power: How much your emperor can control. You cannot have cards in play that would have combined power higher than your emperors.
You cannot play cards if you can't afford them. If your remaining speed pool is 2 then you can only play cards that have 2 speed or less. If you have in play cards that have combined power higher than your emperor, then choose one card and put it into your graveyard. If the power of these cards will still be higher, then repeat the process
Why include such restrictions and costs similar to MtG mana, or Yu-Gi-Oh levels?
To maximise fun, and so that the play won't be determined by "who has better cards"
I have a lot more ideas, like winning conditions, card types, and other things, but I'd like to hear what you think about these first