Using the blood and incense, you mark the inside of an opening no larger than 20ft by 20 ft with sigils. The area must be open on each side and must not be in sunlight, and the side you're facing as you cast the spell is considered the front. Once the spell is completed, the area inside the opening is filled with a wall of fog, identical on both sides. As you cast this spell, you decide if the wall is thin (objects and creatures on the other side are slightly obscured) or thick (objects and creatures on the other side are heavily obscured) and you can give the gate one of the following properties;

Life Sense. While you are within 60 feet of the gate, you are aware of any creature going through the fog, unless that creature's type is construct or undead. When empowered, this property doubles in range and allows you to know the type and size of the creatures going through the gate.

Misty Escape. Until the duration ends, you can cast the spell again as a ritual. Once you do, the two Vapor Gates are connected, and the fronts of each gate now leads to the back of the other gate. Both gates are dispelled if they are more than one mile apart. Only the two gates from the initial cast can be linked in that way. When empowered, this property extends the duration of the spell indefinitely. 

Life's Bane. Unless they are contruct or undead, creatures that go through the gate must make a Constitution saving throw against your spell save DC or suffer 4d6 necrotic damage and they are incapacitated until the start of their next turn. On a success, the creature takes half that much damage, and isn't incapacitated. After making the saving throw, creatures are immune to this effect for 24 hours. When empowered, the creatures also lose maximum hit points equal to the damage they take, and if they fail they also gain one point of exhaustion. The reduction lasts until the creature finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.

This spell ends early if the vapor gate is exposed to sunlight.

At higher levels. For each spell slot level above 4th, you can either add a property, or empower a property the gate already has.