In general, I would look at these two factors when looking to include cards not of your tribe's creature type: Is this creature so strong that it, on its own, is generally stronger than my tribal creatures when they are receiving bonuses and/or empowering my other cards
MTG Arena considers all types of players, from the most casual to the most competitive
That said, there are not all that many different archetypes in black green that want mana creatures except the rock (which is arguably about 6 different archetypes depending on the build) and as Birds of Paradise is a better fixer and ramper the Elves of Deep Shadow are only there to offer redundancy to other better cards
While undoubtedly powerful, it feels counter-intuitive since vampire decks generally go wide
Its so strong that several formats have banned it
In: Moon-Circuit Hacker Out: Skullsnatcher I like the fact that youre not looting on the first try, what with the cheap ninjutsu ability