Your goal is to deploy lots of aggressive creatures as fast as possible. Aim to cast a creature on each of your first three turns to make the most of all tools at your disposal. Your Bestow creatures can buff up your first assault so you can stay on the offensive even if your opponent casts a large defensive creature. Mogis's Marauder is one of the most important weapons in your arsenal. Its ability to give your army intimidate is the best way to win a game if your opponent is able to stabilize and build up a defensive force.
Keeping the pressure on is key. In the early game, you can use your low-cost creature-kill spells like Doom Blade and Ultimate Price to clear a path for your creatures to continue attacking. Bile Blight is a powerful removal spell that can be used to take out multiple creatures at once if you plan correctly.
When sideboarding: Duress = Control,
Pharika's Cure
and
Gift of Orzhova
= Aggro, and
Cremate
= Graveyard.
To push the devotion mechanic to its limits, I might put in Erebos, God of the Dead and if I struggle with card draw I may put in Pain Seer, a low-cost creature that uses the Inspired mechanic to draw extra cards whenever it untaps.
Card Descriptions:
Agent of the Fates
is best when Bestow creatures are casted on it; is a nice creature remover, attacker, and even blocker.
Blood Scrivener is better for later on as far as card draw but also is a good attacker early on.
Crypt Ghast doubles your mana and is your trump card; use extort as often as possible.
Desecration Demon is great creature control while strengthening your offense.
Erebos's Emissary
sacrifices your useless cards to strengthen itself when the time is right; use the Bestow cost.
Herald of Torment
can strengthen your other creatures and increase your offense.
Mogis's Marauder can be a big trump card later on by swinging all creatures with intimidate; use as a blocker in early game.
Pack Rat can multiply and become stronger as well; use this to get creature tokens out if you fall short on blockers.
Rakdos Cackler
is the best one-drop ever; use the Unleash to get a turn one 2/2 and swing turn two. Use as attacker or blocker based on who your playing (attack for red/blue/white and block for green/black).
Rakdos Shred-Freak
is a great attacker; use to swing for 2 on turn two and continue to do this to keep opponent creatures thin.
Spiteful Returned
is best Bestowed and should attack as much as possible so the opponent loses life every time.
Tormented Hero
is a great blocker that should be enchanted so some Extort occurs.
Xathrid Necromancer just sits there so that when it dies (as a blocker) or another human dies you get 2/2 Zombie tokens.
Bile Blight the most fun card ever against token decks.
Doom Blade can be sideboarded and is used against nonblack (duh) decks.
Fated Return IS your trump card. Use to grab the strongest creature in a graveyard (like an 8/8 flyer) and give it indestructible.
Hero's Downfall is great creature (and planeswalker) destruction.
Ultimate Price is best against mono decks and can be sideboarded.
Gift of Orzhova
can be given to your favorite/best creature and creates an offensive powerhouse.
Sideboard uses:
Cremate
would sub out Doom Blade and is meant for flashback, unearth, or rebound spells in red and blue decks.
Dark Betrayal
would sub out Ultimate Price and is meant for black decks.
Duress would sub out
Rakdos Shred-Freak
and is meant for creature destruction and counterspell (black and blue) decks.
Gift of Orzhova
would sub out Swamp and is meant for red and green decks.
Pharika's Cure
would sub out Bile Blight and is meant for creature destruction (black and red) decks.
Staff of the Death Magus
would sub out Xathrid Necromancer and is meant for red decks.