Hey folks, here are some tips that I am using to farm Arenas without any troubles.
It might not be the FASTEST way to get to over 70 kills, but it sure is the safest. Keep in mind that all of my heroes are over level 45. It is super easy to grind up that hight, just give eggs to the team, and with Rogue (for damage boost) grind the Stone Golem boss. It is the fastest kill, gives appro 400 exp, in few hours you can have entire team 45+
Setup one "Time Freeze":
1x Warrior, 2x Mages, 1x Bard.
Warrior: hard tank setup, 2x Lodestone for evasion.
Mages: Timestop, 2x Eye for ~30% no cooldown
Bard: Refreshing song, 2x Eye.
Just Timestop the battlefield all the time. If both Mages go on cooldown, refresh them with Bard. If Bard's Eyes proc, making him not go on Cooldown with refresh song, it's like another full minute of no mobs doing anything.
This setup is tricky if you are VERY unlucky and your Eyes never proc. Do not play Lotto then, it is obvious waste of money for you.
Setup two "Icy Death":
1x Warrior, 2x Mages, 1x Priest
Warrior: same as above.
Mages: Blizzard, 2x Book that reduces cooldowns.
Priest: Heal setup, 2x Book that reduces cooldowns.
Blizzard has 30 sec cooldown by default, lasts 10 seconds. With books, it is on 18 second cooldown. And you got 2 mages, meaning, it is PERMAFROST. You even got a 2 second gap for safety, you do not have to split-second time it.
Entire battlefield slowed down, mages can just portal around and shoot stuff. Take out Archers fast with fireballs and conflagrate, easy as a sunday morning.
Go grind, get those T9 items.