Find the Missing Artifact

The manor is full of undead creatures. The magic of the lich has bound them to the premises. They are locked into different areas of the manor, trapped as the lich is by magical force. The lich has convinced the eager Mandilissimar to brew three different colored potions (red, green, and blue) to unlock the magical barriers and release the undead. The potions themselves only attract undead, but Mandilissimar has also been guided in the creation of a special lantern.

The lantern is an activator for the undead. Led to believe the key to finding the artifact he seeks is tied to the full moon, Mandilissimar has crafted a lantern that gives off an ethereal moonlight. This aura given off by the lantern reanimates the undead when they are within its area of effect. Once active and out of their starting locations, they are fully activated and act accordingly, drawn toward any individual attracting them.

If the lantern is broken or shattered, it explodes in a 10 foot burst of 2d6 necrotic damage. It also instantly activates all of the undead in the manor. Mandilissimar takes 3d6 psychic damage, and snaps (or once he realizes the lantern is awakening undead). He will leave for his ruined tower after this.

There are 32 ghouls, 12 ghasts, and 6 wights trapped within the manor. As the characters move through the house with the lantern, it will trigger the activation of the undead from their trapped locations. Anyone wishing to make an arcana check (DC25) to understand the lantern will know it is responsible for activating the undead. If they suspect it is the case, they can roll their arcana check with advantage.

The undead are scattered throughout the different rooms of the house, so only partial numbers of them are activated at any one time. Once they are activated, they remain active, and will be drawn toward anyone who drank their color of wine - red attracts wights, green attracts ghouls, and blue attracts ghasts. If no one has drunk an attracting color, those monsters roam randomly, seeking out living victims.

The map attached is one I found on Roll20 that I like. I have shaded areas with blue, red and green as starting areas for the undead. There are six red areas, each with 1 wight in the room. For the 6 blue areas, each contains 2 ghasts, with 2 ghouls in each of the 16 green shaded areas. The lantern gives off a magical aura that can pass through walls, so any undead within 20 feet of it are activated whether in line of sight or behind a wall. The numbers are high, but the idea is that only a few will be activated at a time, so the numbers really play out as 5 or 6 encounters. 

The other element of the manor is the small courtyard with a pool, overlooked by a statue. There are two gargoyles perched on either side of the southern door, that appear to be nothing more than statues under inspection. The artifact Mandilissimar seeks is located in a chest concealed beneath the water of the pool. There is a hidden catch on the back of the statue that causes the chest to rise, but also awakens the two gargoyles placed in the room to guard it. Within the chest are the lich's phylactery and a magical tome. The tome is important to the main quest, but will take time to decipher. Mandilissimar can assist with this if he is not mad, but he will need to be cured of his illness and take a long rest before he can gather anything from the text.