To optimize your MTG Athreos, Shroud-Veiled EDH deck for maximum effectiveness in gameplay, focus on including cards that synergize well with Athreos's ability to return creatures from the graveyard to the battlefield. Consider adding cards that generate value from sacrificing creatures, such as Blood Artist or Viscera Seer, and include ways to protect Athreos and your key creatures, like Lightning Greaves or Teysa, Orzhov Scion. Additionally, include a mix of removal spells and card draw to maintain control of the game and keep your strategy going. Regularly playtest and adjust your deck based on your gameplay experience to fine-tune its performance.
In Magic: The Gathering, Athreos, God of Passage's official rulings state that when a creature you control dies, your opponent can choose to either let it go to the graveyard or return it to your hand by paying 3 life. If the opponent chooses not to pay, the creature goes to the graveyard. Additionally, Athreos is not a creature unless your devotion to white and black is high enough.
To maximize the generation of tokens with Athreos in your deck, focus on cards that create multiple creatures at once, such as token-generating spells or creatures with abilities that produce tokens. Additionally, consider including cards that can protect your tokens or make them more resilient to removal. By building a deck with a strong token generation strategy, you can make the most of Athreos's abilities and create a powerful board presence.