Speed/offense Arena set up:
1. High Khatun - 19% Speed aura, turn meter boost, speed buff, some turn meter reduction
2. Skartorsis - attack and crit. rate buff, cleans debuff, slight turn meter boost, AoE A1 with steal buff chance
3. Tayrel - AoE defense debuff, turn meter reduction, possible one target CC
4. Skullcrown - high AoE damage dealer, extra survivability
Works well on auto, reliable in defense too. Core idea is "one hit nuke", but they all have extra build in survivability - Khatun, Skartorsis and Tayrel have good based defense stat that can and must be further extended with proper gear. Skullcrown [Unkilable] can be lifesaver. *edit - hehe, well, this wasn't intentional :)
1. High Khatun - first > party turn meter boost + 30% [Increase SPD].
Must be build for full speed, good accuracy is not bad idea. Boost her defense and don't bother with any offensive capabilities. Both Skartorsis two buffs benefits her and she can help with some extra damage with her second AoE and third A1 hits, but this is just extra, she is not there to do damage. Defense + Support tree work best for her Arena build. Her turn meter boost is only 15%, so that alone can`t do miracles by itself. All other team members must have some good speed too. No need to have her 6/60 and even booked, but will help.
2. Skartorsis - second > 50% [Increase ATK] buff and a 30% [Increase C.RATE] to all party.
Can be build very tanky and probably will be your last man standing. Good Provoke or maybe Stun Set is not bad idea. With good stats can do some extra damage, but he is more useful as supporter that second damage dealer. Good accuracy can help his A1 [Steal Buff] move and high resistance is verry important. Defense + Offense + Support tree can work well in any combinations, depends of how you want to build him. I will definitely go for Offense + Defense for him, but that`s my approach and the way I use him. Depends of your general idea, you may find some other mastery combination more useful to you. No need for heavy book investment, but it will help, especially for that extra steal buff chance.
3. Tayrel - third > AoE 60% [Decrease DEF] AoE.
Full defense build, enough accuracy to make sure that DD debuff will not be resisted. He can`t benefit from Skartorsis attack buff, but he can pull respectful damage anyway. Heavy Force affinity teams can be problematic for you, if you land weak hit and fail to place that DD debuff. I don`t use him in Arena and can`t recommend mastery path for him, but maybe Support + Defense seems more useful for him. Greatly benefit from any book and maxing A2 is just must.
4. Skullcrown - forth > AoE nuke.
If build correctly and Tayrel manage to place that debuff, this may end the fight. Embodiment of glass cannon meaning. Full damage "one hit build". 100% crit. rate, good attack, stack Crit. Damage. Both buffs from Skartorsis benefit her greatly, she has high base Attack stat, good damage modifiers and if you don`t use her as farmer, you can aim to hit only 70% Crit Rate. That will give you extra room to focus on further boosting her Attack and Crit. Damage. Don`t bother with any other stat, except for that speed threshold you need to achieve. Offense + Defense mastery is the best choice for her and Retribution and Deterrence has no real alternative in Support three. If you happen to land that [Weaken] debuff from her A2, consider this as bonus. Maxing A2 for CD reduction helps a lot, but her passive CD reduction usually can`t make a difference in Arena, where fight ends within 2 to 5, 6 turns.
If the battle didn't end here, the enemy will start to buff themselves and debuff your team at this point. Your team second move will consist of High Khatun AoE (she will have attack and crit. rate buff) - which AoE have chance to reduce enemy turn meter by 15% and maybe even finish some very low on health enemy.
If there are debuffs on your team at that point, Scartorsis will clean them and heal and boost the turn meter of those, that has debuff cleaned. It will not be huge heal and boost, but it may stack to noticeable point with Khatun previous turn meter reduction. On Arena, every little move can make a difference.
Tayrel will do his single target hit, that can do good amount of damage, possibly finish someone of his misery :) and if not, will reduce his turn meter. Maybe even stun him if stars and planets are perfectly lined for him.
Skullcrown... well, she has only one job in your team really - to hit people, so let her hit them, if that will make her happy.
This set up can be further improved by replacing some or almost every every one with similar, but better version champion. It is all about the concept behind the speed/offense set up, not about the key champion aroun which you build your team.
High Khatun can be replaced with better Arena Leader - Gorgorab, Lyssandra, Prince Kymar, Arbiter. They all will fit in this set up. Tayrel can be replaced with Stag Knight or Draco and so on.
The moment you start to lose your battles mostly because your team didn't act first is the moment you will have to return to the starting point to improve your gear and overall stats.