Vio and Modus are really easy to play with great success, especially modus as he has a very good escape. Violet can burst down almost any non-tank hero in the game from far, and if they get close and kill her she usually gets a revenge kill with shadow damage or the spawned mr midnight. Also, Gobi is basically "pick him up and you're a pro" imo. His constant armor reduction makes it close to impossible to loose when even just spamming skills, plus he has an escape on a rather short cooldown in worst case. I would argue that any character with stacks is also a bit harder to master, such as Bjorn who really deserves more points on this list.