This is a day one deck I built around The Dark Portal and dragon synergies. It is performing well so far, in particular against Demon Hunter. But the expansion has been out for less than a day, so that may not mean all that much.

Mulligan and Early Turns

Mulligan for your 4-drops: the mana cheats The Dark Portal, Frizz Kindleroost and Escaped Manasaber are what you are looking for, but Twilight Drake is a decent keep if you aren't offered Frizz. If you expect your opponent to develop onto the board early, Dark Skies might be a keep.

If you go first and tap on turn 2 and 3, you'll have 9 cards in hand in turn 4, which is enough to activate the Portal. Twisted Knowledge nets you one card in hand, so that can be an alternative to tapping on a turn 2 or 3 if you're already holding Portal and are just padding your hand.

I prefer to play Frizz as soon as possible: the earlier you play her, the more discounted dragons you'll draw. Playing Portal on turn 5 is fine: there are a lot of 6-drops in the deck, so you may get to use the final mana to summon what you drew.

Game Play Hints

Your AoE (Dark Skies and Crazed Netherwing) hits both sides of the board, so you have to time it carefully to make sure it hits your opponent harder than you. If your opponent has multiple minons, it can be worthwhile to for example coin Netherwing on turn 4 and delay your 4-drop.

If you're playing against a control deck, it can be a good idea to hold on to some of your discounted cards and use them to reload after a board clear.

Healing is provided by Nether Breath and Aranasi Broodmother. Note that the Broodmothers are the only demons in the deck, so if you haven't drawn them both yet, picking Sense Demons from Twisted Knowledge is a nice way to force a heal.

Zzeraku the Warped is fun to play in reaction to Priestess of Fury or Imprisoned Antaen.

Alternatives

Of the expensive cards, I'd say that replacing Frizz Kindleroost, Alexstrasza and Dark Skies would really weaken the deck, but the others could be replaced without problems.

Perhaps Khartut Defender could be added for even more heal. On the other hand, it doesn't apply much pressure, so while it keeps you alive longer, it also gives your opponent more time to kill you.

It would also be interesting to do a highlander-ish version with only duplicates of key cards. While drawing Zephrys the Great from Portal means losing two mana, having a zero-mana wish is extremely flexible. In any case, there are quite a few minions in the deck, so drawing Zephrys wouldn't happen all that often.