This is a casual, Theros and Enchantment-themed, EDH deck. It's primary purpose isn't necessarily abusing Athreos' ability. That said, it is very helpful and can create some neat interactions in the deck.
The most important things to remember are that this is 1.) CASUAL, 2.) MULTIPLAYER, and 3.) a THEMED deck. Because of this, it has quirky interactions that do useful things, but may include sub-optimal cards for the sake of matching the theme.
Of Note: This deck is built from cards I currently own. All suggestions are welcome, however.
THEME
The big thing is enchantments. Everything centers around them. There are 38 Enchantments in total, spread across base enchants, auras, artifacts, and creatures. Because the deck centers around a permanent type, it is also very easy to attain and keep devotion. Thus, Athreos becomes viable as a means to victory.
Most of the non-enchantment cards support the theme. Cards like Mesa Enchantress, Silent Sentinel, Treasury Thrull, and Replenish help maximize the usefulness of your enchantments.
CARD DRAW
This deck tries to use Enchantments and permanents as its main method of card draw. Erebos, God of the Dead and Underworld Connections bring the typical cards-for-life that Black offers. Mesa Enchantress enables you to draw cards just for doing what this deck wants to do. There are a few cars that cycle as well.
REMOVAL
There are different methods of removal and control in this deck. Because of the need for enchantments and devotion, though, some of that removal comes not from spells, but from permanents.
Enchantment-Based Removal/Control:
Banishing Light, Oblivion Ring, Cast Out: These are your primary removal spells that can remove anything you want save for lands and permanents that can't be targeted (Which is why Arcane Lighthouse is in the deck!). They are two fold in that they act as removal and provide devotion for Athreos and Heliod.
Darksteel Mutation: This is the best removal for opposing commanders! Why chance sending them to the graveyard or exiling them when you can make them both useless and immune to removal? This has the potential to take an opposing commander out of the game for good, as they can't even play it again from the command zone again until they find a way to get rid of the enchantment or the commander themselves.
One Thousand Lashes: A better Pacifism that keeps the creature from using activated abilities and slowly drains your opponent.
Soul Snare: Close to an enchantment version of Path to Exile and its ilk. Just another way to exile pesky beaters while triggering Constellation, and adding to Devotion while it waits for a target.
Visara the Dreadful gives the potential of repeated removal. Wrath of God can wipe a board and Extinguish All Hope can do the same while leaving your army of enchantment creatures. Silence the Believers, Path to Exile, and Swords to Plowshares act as spot removal.
Aura of Silence can both prevent your opponents from getting out mana rocks early and destroy a pesky enchantment or artifact later in the game. Sphere of Safety is AMAZING in this deck, as your opponents will often have to pay 5 or more just for a single creature to attack
STRATEGY
The main strategy with this deck is to get your support cards out early and then flood the board with your enchantments that act as removal and disruption. Getting an early Mesa Enchantress out will enable your card draw engine. Blind Obedience can help delay an aggressive deck. Underworld Coinsmith and Grim Guardian make subsequent enchantments come in with bonus drain-life. Other constellation creatures are good early drops as well. This deck acts as a permanent based control deck that builds up for a late game takeover. Disruption and controlling the board as much as possible is your goal early to mid-game. Your commander, Athreos, is another enchantment you want to get on the board early, as he can help give longevity to those smaller enchantment creatures you use early on.
Once you are in a comfortable position, try to lock the board down and become the aggressor. A voltron strategy with Athreos is a good option. Tokens and power/toughness boosts are another avenue to victory. Don't forget that you have means to drain life from the opponent (with extort on Treasury Thrull and Blind Obedience as well as Underworld Coinsmith to help out.
MEANS TO VICTORY
1.) Voltron!!!!!
The number of permanents in this deck leads to an easy time with Devotion (unless, of course, you are playing griefers [sad face]). My favorite thing to do is reach devotion with Athreos and then start enchanting him so that he can survive a board wipe and still remain a creature due to all the auras attached to him!!!
The beauty of including all those "sub-optimal" Bestow cards is that you can use them to enchant Athreos and buff him up for huge commander swings. Ghostblade Eidolon grants double strike. Hopeful Eidolon gives lifelink. Others grant deathtouch and intimidate. Even if an opponent finds a way to get rid of Athreos, all those "auras" fall off and suddenly become an army of small creatures! If you have Spear of Heliod and/or Dictate of Heliod out, that army ain't so small anymore.
Some of these auras that can be placed on Athreos (or even Heliod or Erebos) can double as a ridiculously powerful defense. Enchanting Athreos with Pariah means that you are completely immune to damage until they can either get rid of the god or the aura. Put Soul Link on top of that for the ultimate in Grade-A dickery! That's right, any damage done to you is redirected by Pariah to your indestructible deity and Soul Link causes you to GAIN that much life instead. (Caution: Your friendly neighborhood Red mage will cease being so friendly while he waits to draw that Chaos Warp)
2.) Tokens
Another route to victory in case the Voltron method fails is an army of Tokens. It's a very small sub-theme, but it's enough to surprise and overwhelm your opponents. Grave Titan can easily generate a few tokens. Heliod, God of the Sun can use all that mana generated from Nykthos, Shrine to Nyx to pump out enchantment creature tokens to trigger all of those Constellation cards. Elspeth, Sun's Champion can continue spitting out an army indefinitely. Those tokens you're making get to be a real threat when combined with Spear of Heliod and Dictate of Heliod.
C-C-C-COMBOOOOS!!!
1.) Athreos, God of Passage and Starfield of Nyx
Before anyone gets upset that I'm not using Athreos' incredible static ability, I want to assure you that this is far from the truth. With Starfield of Nyx making all of your other enchantments creatures, Athreos gets double duty. Now those Enchantments can be killed? Okay. I'll just get them all back with Athreos unless you pay 3 life for each. Ta-Da! Getting only creatures back with Athreos? Now who isn't maximizing his potential?
2.) Deserted Temple and Nykthos, Shrine to Nyx
Nykthos can create an incredible amount of mana, but combine that with Deserted Temple and you can double that up. Heliod's Cleric tokens thank you.
3.) Faith Healer and Oblivion Ring
It is possible to permanently exile nonland permanents when using Oblivion Ring. While Faith Healer is out, cast Oblivion Ring. When it's enter the battlefield trigger goes on the stack targeting a permanent for exile, immediately sacrifice it in response. the leaves the battlefield trigger will go onto the stack and then resolve first, returning nothing to the battlefield. Then he enters the battlefield trigger will finally resolve, exiling the permanent it targeted. Since Oblivion Ring is already gone, there is no way for it to leave the battlefield and return the exiled permanent. Thus, you have just permanently exiled whatever it targeted. A neat little trick and one that is sure to anger your opponent from time to time.
CONCLUSION
That's the basics of this deck. There are many more fun interactions in this deck. It's one of those that is totally janky, but surprises you. So much fun to play.