An individual Borg drone loyal to Lore who was captured by the Enterprise and used to manipulate Data's emotions.
Crosis is one of the Borg drones who, after the Borg collective was disrupted by Hugh's individuality, followed Lore. Having become individuals, they came to see Lore as a leader who could give them purpose.
In Descent, Crosis is captured during an attack and held aboard the Enterprise. Through him, Lore sends Data a carrier wave that triggers powerful emotions, allowing Crosis to persuade Data to escape with him and join Lore's cause.