This week I've been building several Hecatomb decks. This is a deck I like to call DG Toolbox. DG stands for Destruction/Greed. Toolbox means you can search for cards that you need in the situation you're in. This is why a lot of cards are included 1x or 2x.
These are the Toolbox core of the deck. They let you search for various other cards.
The FILTH DWELLER and SCEPTER OF OSIRIS are the core of the toolbox in the deck. Besides the many situational One-offs that can be retrieved, there are important cards for the deck, or good value cards in general. Unspeakable Talisman lets you do so much more during your turns, and is most likely to have more value for you than your opponents. Because you get to play more cards due to the retrieving and exhuming.
There are plenty of Ramp cards in the deck to get that sweet additional mana, while still getting board presence. These cards include: Dead Man's Hand and Brain Worm. The earlier mentioned Unspeakable Talisman gives you double mana from every mana card, later on, which gives even more value to the mana ramp in the deck.
Various Relics and Relic Minions have great synergy within this deck. Neural Graft makes your Abomination stronger, for every Relic you have on the field (which can go really fast: dead man's hand + neural graft + hoverdisk is already a big abomination). This will get you board presence even before you get your Toolbox online. Assimilation gives you fantastic and diverse recursion, because there are several minions that have the Relic type, and several important pieces of the deck are also Relic.
Hatcheteer is included in the deck. I don't think he's very good in general, but under conditions he's very much worth playing. If, for example, you can trigger a conditional ability of another minion, or search your deck because of playing him, it's definitely worth paying 1 soul.
You'll see many cards included 1x, which represent the toolbox. Several minions that are considered part of the toolbox are still listed 2x because they somehow have more value for the deck.
Other main cards are also included only twice, but you don't want to play them early game, and don't really need 2 on the board. An important card, that is only included twice is Unspeakable Talismans, because I don't recommend playing her before you have 6 mana. (You'll pay 3 for the talisman, then have 6 mana to do whatever you would have done. You won't lose any mana. Keep in mind your opponent will also get value from this card.) Also scepter of Osiris is very important for the deck, but you don't need more than one on the field.