In this new area, there are four switches around the great room. Each is a phase of the moon (except there's no full moon). You click the panel on a switch until the phase of the moon pertaining to it swings in front of your area where you're standing. This will unlock a bridge allowing you to fight the monsters behind you. The minions are pretty simple, and I stuck to my last deck's build (dots and links/power links). After defeating each set of monsters, a chest will appear containing an over-sized moon shield. You take each moon shield and give it to one of the four giant celestial statues (you click x when in front of it).
Once all four have shields, the way to the boss opens.
Here's the cheat description from the Wizard101central wiki:
That wiki page also shows he does lots of ice and some death magic.
Here's how I built my deck and what I did...
Deck of Reflection:
2 Fire Dragon
2 Rain of Fire
5 Glacial Shield
1 Elemental Trap
Sideboard: 3 Tower Shield
He had a stellar protector with him, so besides the damage-all-opponent spells not triggering his 90% tower shield cheat, it also served to start burning down the minion. Again, the Empowerment spells were great to keep pips up so I could throw big spells sooner. When I had enough pips, and he had no shield, I would throw Gargantuan Efreet. Also, I'd make sure to get a Fuel and an Elemental Trap down, before Efreet went off. I think if I were to do this again, I'd probably go four of each of the Scald and Fire Dragon spells, throw in one or two more Fuels and Elemental Traps, drop the Infallibe (I don't tend to fizzle), cut down the Efreet to one or maybe two, and that should be good.
Of note: he didn't cast any death spells that battle. I did not get out of this battle with full health however.
EDIT: If you can hold off, you can always blade first (which will remove any shields he has on himself) and then put traps on him. However, you should know that Wyldfire counts as a charm in this encounter. I found out the hard way on my last run, removing my Fuel and Elemental Trap I had previously placed on him. Blades actually make sense to use in the deck, as you get to remove his huge tower shield. All that being said, I still had no problem using Empower, various AoE spells, and Gargantuan (now Colossal, since I've learned that).