Hearthpwn

If you can't beat them, join them.

Tried to reach legend with Mage, playing both Naga and Mech, but got tired of getting stomped in this hyper aggro DH meta, with Drek'Thar everywhere.  So I decided to stop fighting a losing battle and join the obvious winner. And it works, got legend with it.

Started with typical Mech Mage build (https://www.vicioussyndicate.com/decks/gateway-mech-mage-2/) and cut what I had to fit Drek'Thar - so from the start no Fireball, Ini Stormcoil, Mothership and Gaia, the Techtonic. Also with reduced number of mechs, and aggro meta, Seascout Operator battlecry proved to difficult to trigger, especially turn 3, so it had to go as well. As much as I like flashy effects of Mothership or Gaia, the Techtonic, these cuts don't hurt that much and you still have plenty of options to get them during the game anyway.

This leaves us with 22 cards and 8 slots to fill:

Drek'Thar - well, obviously. You need to fight fire with fire. Best tempo card in this meta. Can also trigger Security Automaton and Mecha-Shark.

Arcane Intellect - mostly for later refill, rarely useful turn 3 (unless you play against slower decks).

Impatient Shopkeep - with little removal, rush can let you deal with small but dangerous threats. Also great with Drek'Thar, but mostly for tradeable ability.

Mankrik - good 3drop, nice body for Drek'Thar to fetch.

Rustrot Viper - weapon removal is very essential in this meta - DH, Warrior, Paladin. Also tradeable and good Drek'Thar target.

I must admit, I am not 100% sure about these choices, you might also consider:

Runed Orb - early removal, chance for another Seafloor Gateway

Smothering Starfish - silence can be really important

Amplified Snowflurry - great tempo card against DH

But for now this list seems to work best for me. You play this deck like standard Mech Mage (with some additional options) - either going for early pressure or collecting mechs for otk turn depending on match-up. DH is still difficult, but from my experience, much more beatable than with the standard list - and other match-ups don't seem to be worse.

edit: trying now version with Fireball and Runed Orb instead of Arcane Intellect and Impatient Shopkeep, will edit deck if this will improve the results.