It was pretty ridiculous, I'm still somewhat in shock. While the deck tries to do it at some point as a way of winning, I've never been able to do it, and I NEVER envisioned being able to do it turn four.
It involved the following.
Turn three, Cast Zur the Enchanter.
Turn four, had the following cards in hand: Gold Myr (I think), Mox Opal, Ponder... I had something like 5-6 mana on the deck due to artifacts (but I remembered needing the Myr to make Opal work due to its metalcraft requirement)... top decked Erayo, Soratami Ascendant. Proceeded to Gold Myr, Mox Opal, Eryao and then Ponder as fourth spell of the turn, which flipped Erayo to the legendary enchantment Erayo's Essence. Then I went to attack with Zur, and searched my deck for Arcane Laboratory using Zur's 'on attack' ability.
The one thing I will say is that Cavern of Souls could have worked if you had it out, but it was only a matter of a turn or two before I'd start drawing obscene cards via Necropotence, and making Zur unblockable via Steel of the Godhead and tossing Empyrial Armor on him.