Historian Rogue

You are a skilled historian who research, analyze, interpret, and write about events, terrains, and even creatures from the past by studying historical documents and sources, using the information to give you advantage on executing your plans. Unlike other Rogues Archetypes, you prefer the sharpness of your mind over your daggers or swords, for knowledge is the deadliest weapon.

Student of The Past

Starting at 3rd level, you gain proficiency in the (History) skill if you don't already have it. Your proficiency bonus is doubled for any ability check you make with that skill. You also learn four languages of your choice.

I Read About You!

When you choose this archetype at 3rd level, you gain the ability to analyze the creatures you are fighting. When you deal your Sneak Attack damage to a creature, you instantly know that creature's type, all of its movement speed (if any), all of the languages it understands (if any), and its challenge rating or class levels (if any).

Additionally, after dealing your Sneak Attack damage to a creature on your turn, you can force that creature to make a Constitution saving throw against a DC equal to 8 + your proficiency bonus + your Intelligence modifier. If the save fails, that creature’s speed becomes 0, and it can’t benefit from any bonus to its speed until the end of its next turn for you successfully learned the creature's weak point. 

You can reduce a creature's speed this way, a number of times equal to your Intelligence modifier (a minimum of once). You regain all expended uses when you finish a short or long rest. 

Smart Decision

Starting at 9th level, years of learning about combat history granted you an enhanced version of your Cunning Action feature. When you use your Cunning Action feature, you gain temporary hit points equal to one plus your Intelligence modifier (minimum of one). While you have these temporary hit points granted by this feature, any Attack rolls against you are at disadvantage for you have prepared yourself against incoming blows.

Expert Learner

By 13th level, you have seen and learned from lots of people and events. Choose one skill in which you have proficiency. You gain expertise with that skill, which means your proficiency bonus is doubled for any ability check you make with it.

Additionally, whenever you finish a short or long rest, you can gain one skill or tool proficiency of your choice which you lack, as the years of reading and learning have taught you to be prepared for any challenges ahead. You lose this proficiency when you use this feature to choose a different proficiency that you lack.

Intelligent Strike

When you reach 17th level, you have known lots of creatures and their weak points. When you use your I Read About You! feature, instead of reducing its movement speed, the creature who fails the saving throw is now (Stunned) until the end of its next turn. It also takes extra 3d6 of Sneak Attack damage, and halved if it succeeds.