Are they playable

Abundance Agent's Toolkit Alhammarret's Archive Alms Collector Archmage Ascension Artist's Talent Asmodeus the Archfiend Blood Scrivener Case of the Pilfered Proof Dakmor Salvage Dark Dabbling Darkblast Enduring Renewal Eruth, Tormented Prophet Family's Favor Fasting First-Sphere Gargantua Fisher's Talent Flotsam // Jetsam Forbidden Crypt Golgari Brownscale Golgari Grave-Troll Golgari Thug Grave-Shell Scarab Greater Mossdog Heroic Sacrifice High Score Hullbreacher Immortal Coil Island Sanctuary Izzet Generatorium Jace, Wielder of Mysteries Jaya Ballard Laboratory Maniac Lashknife Barrier Leader, Super-Genius Lich Life from the Loam Living Conundrum Mangara's Tome Meat Locker // Drowned Diner Moldervine Cloak Necrodominance Necroplasm Nemata, Primeval Warden Nightmare Void Notion Thief Obstinate Familiar Ormos, Archive Keeper Out of the Tombs Ozolith, the Shattered Spire Parallel Thoughts Peregrin Took Personal Decoy (playtest) Phial of Galadriel Plagiarize Pursuit of Knowledge Quantum Riddler Ral's Vanguard (playtest) Retriever Phoenix Rigo, Streetwise Mentor Rime Chill Sages of the Anima Scrapwork Mutt Scrapwork Rager Shambling Shell Sharae of Numbing Depths Shenanigans Snake Umbra

Instant Removal (CTRL to add secondary) Tutor Nature's Rhythm Search your library for a creature card with mana value X or less, put it onto the battlefield, then shuffle
Flashback will probably still be the most dominant way to take advantage of Sevinne, with a much greater saturation of cards with the mechanic (plus cards that favorably interact with flashback, like Burning Vengeance or Secrets of the Dead)
The white feathered wings stretch across most of the card against a near-black background, giving Mega Absol an almost Batman-esque pose
Keep playing your deck, discover what you like best about it, and become the best player you know