Demons

 Now you are ready to build a demon team. A demon team is another great choice for a first legendary team. They have enough strong characters on the team that you can accomplish most anything in the game before unlocking their legendary. Outside of the legendary event, this team has two legendaries and is one of the strongest arena teams in the game.

Bench warmers

Megawheel- He's Mega "Meh". When facing this character, I often just ignore him until the end. I'd rather run no defensive characters then level this guy up.

Core Team

Kaira

Kaira has the ability to turn the non tanks of the team invisible. This is huge, it also gives the tanks counterattack which is synergistic with Kirri. Beyond that she has an abilty block and hits with an AOE mega strike.

Runes: You have two options for 4 of your runes, either damage or speed. Lower speed could be made up by a singer lead, which means you want your hits to deal more damage, but it's up to you. Your other two runes should be either crit or potency. I'd suggest crit.

Artifact: There are a couple artifacts that involve benefiting from invisibility or granting invisibility that I find quite useful on Kaira. When it comes to stats, you likely want to increase damage, crit, or potency (so any offense). I feel the defense options are all fairly even as well.  

Kirri

Kirri is simply an amazing tank. Many reviewers are calling her the strongest defender in the game and she lives up to it. She has really short windows of taunt downtime, making it really difficult to plan around. She has good self healing that keeps her tanking longer than other tanks. 

Runes: Kirri benefits from most stats. That being said, I'd suggest fully armor set runes. Tenacity is another stat that you don't want to shy away from, and I would not fault anyone going that route. At first I thought potency would be really great, but it turned out less important to me in testing. Her debuffs are good, but they don't define her. I would go with more defensive stats over potency. You also want shield on your runes' stats when you can find them.

Artifacts: For raw stats I suggest armor, tenacity, or shield for your defensive stat and attack power for the offensive stat. There are many good artifact secondary abilities you may want to try out. I suggest increasing defense, good healing over time, or removing/reducing debuffs. My current artifact for Kirri heals her at the beginning of each turn.

Slinger

Slinger has the second best lead in the game. Crits happen quite often, thus his increase to your teams turn meter will give you a huge advantage. The extra 20% health on top of this isn't too terrible either. Even without considering his leadership, he would be a contender for the team. His basic attack is a turn meter reducer, which is always a great bonus. He is able to weaking a strong opposing attacker, and his AoE is great for removing buffs from the opposing team.

Runes: You have two solid options for Slinger: Crit or Potency. The turn reducer and attack debuff utilize potency, while the AoE buff remover depends on crit. Personally, I find that the targets of the attack debuff don't often stack high enough potency to resist. I like removing buffs, especially taunt or invisibility from my opponents. This is why I stacked crit.

Artifacts: The artifact I'm using is mostly there for the increase to crit chance. It also increases life steal, which is fine, but I think increasing health or armor would benefit him more. As I advance, I'll likely change this to something that helps him survive a bit more. 

Xantara

Xantara is regarded by many as one of the strongest healers in the game. The key factor is that she heals someone every turn, often while also dealing good damage. Her ability cooldown reducer also adds some variety to the games and has some powerful effects, such as allowing 0 downtime invisibility or taunts.

Runes: I suggest Damage & crit sets, speed in the top right, damage in the top left and bottom. You really want Xantara to hit as hard and often as possible. I'd look for speed secondaries where I could find them as well. These will serve you better than a speed set. 

Artifacts: I like the artifact I'm using on Xantara and that is the Caustic Broth that give her a 15% chance to turn invisible when attacking. It also has a bonus to damage and health, which are probably the best stats to look for.

Shadar

Shadar is a great damage dealer and support character for this team. His ability to grant the team half their turn meter cannot be underestimated and will often let the team take more turns than your opposing forces. I strait up stun on an opposing character at the right time will break the match in your favor. His primary attack also often helps you focus down a target.  

Runes: For Shadar I went with Speed and potency sets. You want speed as high as possible to trigger the speed increase for the team as many times as possible and get more attacks in. Potency is next because his debuffs are great at controlling the battlefield.

Artifacts: I am using an a potency and health increasing artifact that also grants life steal a couple times. Potency is the key for me on this artifact and I'll be on the lookout for a potency increasing artifact with a cooler ability as I progress. 

Substitutes 

Buff

Buff is powerful. If you have him, use him over slinger. His leadership ability is the strongest in the game. +30 speed and 30% tenacity would be great, but the chance to reduce the target's turn meter on all of your team just breaks the game. If that wasn't enough, his abilities make him a great, hard to kill support character. There is a lot of randomness, but it's mostly good no mater what random comes up.

Runes: If I had Buff, I would go with speed everywhere I could put it and potency as my top priorities. You want him to take alot of turns and throw out as many buffs and debuffs as you can, and you want those debuffs to land.

Artifacts: I'd probably go with the best artifact that increases potency I could find. There is one that also heals when he dodges, which would be kinda insane here.

Puncherface

Puncherface is my ideal choice if I couldn't make the above team in time for the General Mordoc event. He's super fast and can deal a good bit of damage. He just doesn't have the control effects of Shadar that are needed in that spot. Granting taunt to non tanks is a nice technique to get around characters like an opposing Kirri though.

Runes: I would go with speed on puncherface. He has an high speed already, but taking it from high to extreme would be the key to making this character work. 

Artifacts: The most important thing is to find an artifact that isn't limited to a short number of his turns. 

Venomate

Venomate is the other choice if you cant form the team above. The reason you run him is because of synergy with Kaira. He also has some synergy with Kirri. Overall, I think the synergy does not make up for a weaker character than using Puncherface, and definitely not over using anyone in the main team. He could be strong in a dedicated poison use team, if that becomes a thing.

Runes: Like most, Venomate wants speed. In this case it's because he wants to apply as many poisons as he can to buff up himself and Kaira. This being said he also needs potency wherever you have room for it.

Artifacts: You wont go wrong with an artifact that increases potency or has a cool effect when applying a debuff. 

Beyond the Demon restriction

The demon team is one that loves to have as many demons on the field as possible. Buff and Slinger both specify demons on their leadership, Shadar gets stronger with more demons. There is also a ton of synergy between characters. This means the only non demon that would benefit the team drastically is Mor'Doom. Mor'Doom is an honorary demon as he summons a bunch of demons. He really feels custom made for this team. When adding him to this team he should probably take Xantara's place. He is a bit of a support character and some of the demons he summons heal the party. Buff leading Kirri, Mor'Doom, Kaira, and Shadar is among the strongest teams as of writing this post.