There are many aspects of a playable card here, so let's start with the obvious, the Darkness typing
Theres a lot of established heuristics on this subject, and a few points I can toss in to help you construct an optimal mana base for Standard, Modern, Pioneer, or whatever MTG format you prefer
This goes up a bit as well based on how much of an improvement having this is to the ability to keep a hand meaning most mulligans will occur on hands without this in them
Den of the Bugbear and Sokenzan, Crucible of Defiance add some 1/1 bodies to the board, while Kher Keep is pretty free to play here and gives you a repeatable token-making engine for effects like Goblin Bombardment and Impact Tremors
This card also has Proliferate, meaning you can choose any trait that you or your opponent have, and add one to its count
[-3]: You may cast target instant or sorcery card from your graveyard this turn