Check out the video here: https://youtu.be/jID6eZBj7TM
Whitemoon decks have been around for some time, but the addition of Sanctum Guard from the Winter War set just upped its consistency and power level considerably.
Since the damage dealt through Arena's ability is non-combat damage, warded minions, like the Guard, don't take damage when the opposing minion strikes it. So it becomes a removal machine that can't be damaged by spells or abilities, and can't be bounced because of that last line of text. He is one tough nut for your opponent to crack.
We have other warded minions such as Raziel and Celestial Dragon to drop on the Arena. Master of Shadows is immortal, but deadly does not work with the Arena, so he's better if someone else wins a few battles on it first (honestly, I'll probably end up cutting him since he's aggressively mediocre). Even if you don't have a warded minion available, we have Mend as our power so heal them up and continue decimating your opponent's board.
The rest is a typical orange purple swarm type of strategy. This deck can go wide, but you can use that swarm to play defensively until you get your combo pieces together, or aggressively to push damage through. But try and keep Insurance Broker alive and well. With all the trades you'll be making, she can easily draw you at least a few cards every game.
And if all else fails, Armageddon Angel is happy to be your friend.
One other important note, the life tap from Sword Saint's biting blade also does not work with the Arena, so don't get any dreams of gaining 100 life or anything like that.