The Nine Pieces

Nine-Fingers, Captain Spark, and Klaus have entered into a race to collect nine pieces of a whole. Each was given a different instruction; to unite, to consume, to assimilate.
The unusually large bird has a vested interest in the outcome of the race, and traded Klaus' temporary abstaining in the race for their freedom from the Ethereal plane. However, there appears to be rules in how much involvement it can have.
Fargo is able to hold Captain Spark's collected pieces, amplifying Spark's Tentacle of the Deep feature.
Nine-Fingers is able to eat the collected pieces, amplifying his Dredge Line feature.
The Little Crow is able to detect the nearby presence of pieces, and identify what is and isn't a piece, although this sense can be blocked or hindered.
Klaus has adopted a strange Gooze as their companion. It's intentions are unclear, but it has been verified as not being a piece.
The False Rictavio of Vallaki was one piece, defeated by the combined efforts of the heroes and Ezmeralda D'Avenir. It took on the features of an Oblex, consuming Rudolph van Richten's memories, and making copies of itself. It was consumed by Nine-Fingers, and grants him the powers of duplicity.
The Arm of Izek Strazni was one piece, defeated by Captain Spark and Dusk during the coup of Vallaki. It was able to manifest and control fire. It was absorbed by Fargo, and grants Spark an aspect of fire.
The heroes encountered a strange bipedal deer in the town of Barovia, which attacked them in the Burgomaster's mansion. It is able to squeeze through tiny spaces, and alter it's size a shape. They encountered it again in Jenny Greenteeth's shop, and believe it has taken Ismark Kolyanovich. It seems to have a strange effect over woodland creatures.
The heroes are aware that there is a piece in Krezk, but are unable to pinpoint its current location, due to intereference.
The heroes pursued a piece from the western reaches of Barovia, all the way to Lake Zarovich. They know it is incredibly large in size, but are uncertain of any other properties.