Update 12/19/19

After extensive testing, I've determined that Elemental Allies doesn't go off often enough to warrant inclusion in the deck. Even when the deck is still playing Azerite Elemental, it took me a LOT of games to ever see a benefit from this card. Shame, but not surprising.

Violet Spellwing, on the other hand, almost always feels good to play -- but I'm still having a hard time figuring out which cards to cut from the "classic" deck to make room for it. I'd miss pretty much any of them. Currently, I'm thinking the least important cards in the deck (in this meta) are Arcane Explosion and Azerite Elemental, so I've cut those for Violet Spellwings. Azerite seldom "went off," to be fair, and was often too slow and became a dead card. (But it was SO much fun when it did "go off.")

Update 12/6/19

Flamewakers rotated back out, so I'm putting this deck back to its classic version with Azerite Elemental and Kirin Tor Tricaster. And I'm not sad about it. Yeah, the deck was more powerful with Flamewakers, but other decks gained even more from their broken cards like Mysterious Challenger and Thaurissan.

Looking forward to improving the deck even more with Descent of Dragons -- I think Violet Spellwing and maybe even Elemental Allies will make the cut.

Update 11/29/19

I quit Hearthstone for a couple months, but when I still play, this is my main deck all over again. I'll go back to the "classic" version of it (with Azerite Elemental and Kirin Tor Tricaster) soon, but for now, Flamewaker is back in standard and replaces those two cards.

Update 8/7/19

Although I've been trying out a lot of new decks since the expansion hit yesterday, this deck (with no new cards) is actually the most successful thing I have in the current meta. It seems to do really well against experimental decks.

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Still loving this deck that I've been playing since RoS came out, on the rare occasions that I play Constructed.

I can't claim that it's likely to go higher than 51% on Ladder, but the games are quick and the wins are fun.

Mulligan Guide

Always Keep:

Spellzerker, Sorcerer's Apprentice, Mana Reservoir, Spellbook Binder, Arcane Watcher, Violet Spellwing

Never Keep:

Frostbolt, Fireball, Pyroblast, Arcane Intellect, Stargazer Luna

Sometimes Keep:

Ray of Frost, Arcane Missiles, Shooting Star - You will usually keep these, but it depends on what class your opponent is playing and what kind of matchup you therefore expect. If your opponent is likely playing a control deck that won't play early minions, you may mulligan these removal cards. Shooting Star in particular should only be kept against classes that are likely to go wide early.

Bloodmage Thalnos - Only keep if you have other cards that can benefit early from his Spell Damage; i.e. if you have Arcane Watcher, or if you have Spellbook Binder and your opponent isn't likely to be able to take out Bloodmage between when you play him and when you play Spellbook Binder. Usually, Thalnos will get mulligan'd.

Cosmic Anomaly, Kirin Tor Tricaster - Only keep if you have Arcane Watcher, no other way to activate it, and no Coin. Even then, consider throwing these back and trusting the cards to give you another source of Spell Damage.

Strategy

Go for early chip damage aggressively using your minions. If you start with The Coin, you will probably use it on Turn 1 to coin out a 2-drop. The exceptions are when you have a Violet Spellwing to play on 1, or you are specifically saving The Coin to play an Arcane Watcher on 2. (Ideally, you will have a way to activate that Arcane Watcher on 3 already in hand.)

Use minion-targeting removals (Shooting Star, Ray of Frost, Arcane Missiles) liberally and early to keep your opponent's board clear. If you can snowball the board for 1 more turn to get 3 more face damage in, that's often worth playing your removal. You're not going to be able to keep a big hand of cards in reserve most games; you must be willing to enter Topdeck Mode and trust in the heart of the cards, that the cards you topdeck will be the ones you need.

As opposed to the minion-targeting removals, be stingy with Frostbolts and Fireballs until they represent lethal damage (as they very often will). Occasionally you'll have to use them early, e.g. to freeze your opponent's weapon to preserve board control or to clear a particularly threatening minion (like a Mountain Giant that's about to get hit by Conjurer's Calling). On even rarer occasions, you may play these cards just because you have a lot of Spell Damage out that you're unlikely to keep until next turn. But usually, your wins will come through a burst of Burn to your opponent's face.