This is the highlander Mage deck I've been running on ladder around Rank 7 (EU) with great success.
It's shown no signs of slowing down and doesn't seem to have any hopeless matchups and many strong ones.
Zephrys the Great is an extremely strong card and this list is designed to be able to play him more than once in slower matchups.
We achieve this by either Getting another copy with Barista Lynchen (hopefully with some other strong Battlecry cards on the board although Zephrys the Great is strong enough to copy on his own) or by the combo of Archmage Arugal + Sandbinder that will either draw you Zephrys the Great and a copy or Siamat and a copy or Mountain Giant and a copy.
Zephrys the Great is usually the preferred pull but I think you will agree that drawing two Giants or Siamats is never going to feel bad.
Reno the Relicologist has seen some mixed responses from the community but is still a strong option here, and can clear token boards or a big threat on his own and often get you back in the game if things are going wrong.
Your hand is often quite full with a lot of cards replacing themselves or drawing so Astromancer is another strong choice in this deck and can be a great target for Barista with whatever it summons.
Luna's Pocket Galaxy was hopeless at 7 mana but is now a very playable card at 5 and if you're up against a slower deck it's often worth keeping off the mulligan if you can play it on 5 without being too far behind then your opponent is in for a really bad time.
Conjurer's Calling is a completely busted card. I think it would be viable without the Twinspell keyword. It's that strong.
Giant is the preferred target but with a lot of big minions in this deck don't be shy about throwing it down on anything that costs 6 and above if you haven't drawn your giant.
Puzzle Box of Yogg-Saron is a super fun card that can swing a game or finish a stubborn opponent on its own.
With the Naga Sand Witch , we can reduce our Pyroblast ,Puzzle Box of Yogg-Saron, Blizzard and Flamestrike by slapping a 5/5 body for 5 on the board. With big spells, the Sunreaver Warmage is an easy include and stays active after the discount.
That's an incredibly good deal and a huge discount that can swing games.
Arcane Keysmith: I don't think I've played this once without it giving me the Flame Ward option. Bye, bye aggro.
Vulpera Scoundrel This card is bonkers. Has impressed me a LOT in the games I've played. You can find really useful spells off of it and it has been fantastic in all the games I've played with it.
Warrior: Something has to go badly wrong to lose against Warrior. They can't cope with this deck.
Priest: The quest priests I've played just get overwhelmed before they can get online and start fighting back usually. This deck is swing play after swing play.
Shaman: The Shaman quest is NUTS and this is a tough matchup but in no way unwinnable. I'm around 50/50 with the ones I've played against.
Druid: Another very strong quest for Druid but this deck should be favoured
Warlock: We have a lot of zoo control options here so unless they go lackey mad with their quest this is usually favoured.
Paladin: The reborn decks I've come up against are a pain, as they can create very sticky boards that spiral out of control quickly but again, it's far from unwinnable.
Hunter: I haven't seen a ton of them on the ladder but I think this deck can keep up with their aggression.
These are EARLY days in the meta and this deck is expensive. Don't go wasting all your dust if you don't have a lot on this deck since you should wait for the meta to settle first.
This deck will probably stay competitive though if I had to guess. It had a lot of aggro tools and insane value in the long game.
It really doesn't have a lot of weaknesses even with the one of restriction. There are some really strong cards this expansion (and a lot of them) which makes Highlander decks very viable.
If you have the cards or dust to burn though, this is one of the most fun decks out there. Good luck!