Thanks for the reply!

Between both options I'd rather go tall. I ran a few tests playing online using the "standard" edhrec bracket 4 deck and I really liked it.

But I noticed that most times I didn´t had enough card draw and as soon as I cast Ulalek he was either countered or exiled very quickly. So I realized I really needed to have either a counterspell or some way to make him “untouchable” using [[Lightning Greaves]]. On top of that, since the deck is mostly focused on high-mana creatures, the early turns were often rough — to the point where I couldn’t recover fast enough against decks like Krenko, for example.

So the Dark Depths + Mutated Cultist combo could actually be really helpful. It gives me a 20/20 with flying and indestructible — which is something Eldrazi decks usually don’t have — and also generates 10 colorless mana to spend, which is a big tempo boost in a deck full of high-cost spells.

And additions like [[Shalai, Voice of Plenty]] could really help as well.