The most important aspect is to ensure your win condition needs cards in the graveyard
Were not playing it on turn 1 that often, but its easy to play it and something else on turn 2 or 3
Return will also be a more useful card in gameplay situations than people realize with the ability to exile a key card from your opponents graveyard
Related Wayta, Trainer Prodigy is the decks alt Commander
However, in decks that can really take advantage of eternalize then it gets much better: Self-Mill decks like Sidisi, Brood Tyrant should consider this, but best of all Populate decks like Ghired, Conclave Exile are going to love it, as it's one of the best populate targets
Creatures that enter attacking are never declared as attackers, and as such, they won't cause Demonic Covenant's first ability to trigger