However, I was farming today and playing around with random lineups and discovered that if a hero with a fiend is killed by Skadi’s special, two frost stacks are created per death.
Well, the main difference would be that unlike Ureus that have it’s special secondary effects act on heroes who hold a minion/fiend Skadi needs to either kill a hero/minion to put her stacks, and that fiends can’t be killed by her special skill (unless she would somehow remove them).