There are two paintings and one blueprint to collect.

In the alternate present you'll meet civilians, including workers who will turn hostile if provoked. The past version is crawling with guards and elite guards and a few hounds. The present version of the mansion is home to one rat swarm, two hounds, two nestkeepers and numerous bloodflies. Under the Table is the only one you can lock yourself out of with your actions.

The other special actions - Under the Table, Leaky Basement and Collapsed Balcony - are all performed in the past. You will also unlock A Mine Made Whole and A Better Today by unlocking the alternate present. There are two ways through the door: finding the combination and breaking in through the alternate present timeline, which awards the Temporal Investigator special action. The key objective is to enter Stilton's study and observe the events of the past that took place there.

Optionally, you can open another timeline - an alternate present - which permanently replaces the original game state. Additionally, certain actions in the past will shape the present. The key mechanic in this mission is the ability to move between the present and the past, allowing you to, for example, pass through doors that are blocked in one timeline but not the other. Supernatural powers are disabled here, although the Heart still functions. The map above shows the layout of Stilton's mansion here's the key-free clean version for your reference.

Painting: The Torturer’s Quaternionic Groan.

Painting: The Commutative Rats and the Weeper.

Dishonored 2 still has some tricks to play.

Dishonored 2 mission 7 killing stilton