It may seem a little odd that the deck only has three Dark Depths, but once you look at all the searching cards, it makes sense. Crop Rotation is by far the fastest, although most costly, with Into the North, Sylvan Scrying, and Expedition Map coming in at two and three mana, respectively. Because of all the land searching (another common theme this week), this deck even gets to play a couple sweet tutor targets. Sejiri Steppe combines with Crop Rotation for a build-your-own Blessed Breath, and the sideboard Bojuka Bog and Karakas are both powerful hate cards.
Wasteland is public enemy number one, which is why the deck has four Pithing Needles main deck. Playing a Needle on Wasteland isn't an uncommon turn-one play, even in the dark, just because of how commonly played the card is and how devastating it is to the combo. Crucible of Worlds offers another way to get around Wasteland, and lets the deck reassemble the combo if the Avatar is dealt with somehow.
Because Swords to Plowshares exists, there are matchups where attacking with an Avatar token isn't going to be enough. For that, the deck has Fling, which also conveniently can speed up the clock by a turn sometimes. Between Fling, the full eight Spirit Guides, Lotus Petal, and Ancient Tomb, it isn't unreasonable for this deck to kill as early as turn three (or two with an absolutely absurd draw).