If you choose not to (or can't) cast the card, it remains exiled with no time counters on it, and it's no longer suspended
Improving color fixing from lands can also help to cast the five drop budget Cavalier Elementals who have nice ETB trigger and die trigger, that's good with Muldrotha
The only thing missing is mana generation, which Warmaster even contributes to when combined with Heritage Druid
Oh wait, did I say creature
Araumi of the Dead Tide Ashiok, Dream Render Ashiok, Nightmare Muse Ashiok, Nightmare Weaver Azula, Cunning Usurper Bane Alley Broker Call of the Nightwing Circu, Dimir Lobotomist Corpse Cobble Covetous Urge Deny Reality Dihada's Ploy Dimir Doppelganger Dralnu, Lich Lord Emet-Selch of the Third Seat Etherium Abomination Etrata, Deadly Fugitive Etrata, the Silencer Flotsam // Jetsam Grma, Saruman's Footman Hades, Sorcerer of Eld Halo Forager Hama, the Bloodbender Hidetsugu and Kairi Hostage Taker Invasion of Amonkhet Kang Prime Kathari Remnant Kavaero, Mind-Bitten King Narfi's Betrayal Kotose, the Silent Spider Krang & Shredder Lazav, Familiar Stranger Lazav, Wearer of Faces Lobotomy Lochmere Serpent Ludevic, Necrogenius Mirko, Obsessive Theorist Mnemonic Betrayal Morbius the Living Vampire Paranoid Delusions Possessed Skaab Psychatog Psychic Frog Psychic Intrusion Ramirez DePietro, Pillager Rassilon, the War President Reap Intellect Rogue Class Rona, Disciple of Gix Sealed Fate Siphon Insight Skv'x the Augmenter Superior Spider-Man Symbiote Spider-Man Taigam, Sidisi's Hand Tasha, the Witch Queen Tearle, Entropic Hunger Tezzeret, Master of the Bridge The Master, Formed Anew The Scarab God Thief of Sanity Uchbenbak, the Great Mistake Ulamog's Nullifier Ultimecia, Time Sorceress Umbris, Fear Manifest Unmoored Ego Vohar, Vodalian Desecrator Vren, the Relentless Whispering Madness Winter, Cursed Rider Wrexial, the Risen Deep
It is easy to see this card in a Mono Black deck, but Dark Prophecy has a lot of potential even in decks with other colors as well, as long as they interact with creature death
