Hearthpwn

I honestly think this is one of the sicker Mecha'thun decks, because it is possible to pull of your Mecha'thun by turn 6(!!), and you can reliably get it done before turn 10.

The combo is Wild Pyromancer + Mecha'thun + Equality. This works since your Mecha'thun will never cost more than 3, as long as it's drawn using Prismatic Lens. (If you get Mecha'thun in your hand, well, sucks to be you..)

As long as you have either Wild Pyromancer or Hemet, Jungle Hunter in your hand, you can safely use your first Prismatic Lens, knowing that it'll be a 50% chance of drawing (and also reducing the cost of) Mecha'thun. If you happen to draw Wild Pyromancer/Hemet, Jungle Hunter instead of Mecha'thun on your first Prismatic Lens, simply wait until you get your next lens in hand and pray to the Gods that you don't draw Mecha'thun first..

Once you have Hemet, Jungle Hunter in hand, either use a Prismatic Lenses to get a Wild Pyromancer in hand, or draw it manually. Then draw 'til you are holding an Equality, pop Hemet, dump your remaining Prismatic Lens and pull of your combo. The safest would probably be to wait with Hemet until you've drawn Mecha'thun from Prismatic Lens, because this reduces the chance of him being drawn manually.

I'm doing some testing with this deck atm, seems fun. I'm considering putting in 2x Crystologyto tutor out 2x Galvanizer, but I honestly don't know how they would help.

I'm also considering putting in a one-of Hammer of Wrath, making it possible to pull of the combo with Mecha'thun + Dark Conviction + Hammer of Wrath, and also leaves you with one extra spell in your deck post-hemet, making it possible to Hemet early as long as you have a Dark Conviction in your hand and you feel confident (read: ballsy) that you aren't going to draw Mecha'thun before your two Prismatic Lenses + Hammer of Wrath

EDIT: 

For those wondering, the exact way to pull of the combo by turn 6 would be:

Start with the coin. Mulligan into Wild Pyromancer + Equality + Prismatic Lens.

Turn 1 and 2: Dump excess cards.

Turn 3: coin + Prismatic Lens, draw Mecha'thun and any 1 cost spell.

Turn 4: Draw Prismatic Lens, play Prismatic Lens and draw Hemet, Jungle Hunter and any 1 cost spell

Turn 5: Play Hemet, Jungle Hunter + any other cards you're holding except the combo

Turn 6: Play Wild Pyromancer + Mecha'thun (for 1 mana)  + Equality.