Most of the 4th classes I've seen have focused purely around stuff that sounds cool, but there is no logic to it. For the most part, it is just titan 2 or warlock 2. Other aspects need to be considered. - Each class is based of a defensive stat. Warlock: recover lost health (recovery). Titan: absorb its (armor). Hunter: don't get hit in the first place (agility). You need to consider a 4th defensive stat or find a way to have a perfectly balanced class. (You'll probably have better luck with the fourth stat.) - Right now there are 3 classes with two subclasses. Each subclass is based of one of 3 light elements. With four classes, two subclasses won't cut it. The class will need 3 subclasses which cover 3 of 4 elements. Yes, I'm telling you to make up another element. After all, the other classes need an additional subclass now. - Give them relevance to the story and the wall of the Last City. Give them behaviors, hobbies, characteristics, etc. They need to smoothly fit in with the others. Warlocks are calm and tend study in the walls. Titans are fearless and guard the walls. Hunters are adventurous and hunt outside of the walls. What about number 4? - Don't just try to come up with the coolest sounding super, melee, jump, or grenade ability in the world. Be realistic. A titan isn't going to shoot a giant laser out of his hands. A hunter isn't going to become the incredible hulk. Whatever number 4 is should have abilities that fit his description. Also, don't make him/her overpowered. It stops being fun at that point. - With three classes came three races. Why not make a 4th race to fit in the mix. Just like with the class, make sure it fits in smoothly. Also, be more creative than 'Good Vex' or 'Risen Fallen' or something like that. - Try your absolute best to be different from the other three but still fit in the game. I'll try my best to keep this list growing.