A 4/4 creature for 5 is a reasonable rate as well, though as with most of blacks best mana doublers, being a creature is a pretty significant drawback with the amount of spot removal and board wipes flying around
If they are amazing in Type Four or Five Color but less so in Commander, then they may not make this list at all

Eye of Ojer Taq Eyeblight Cullers Fabrication Foundry Faces of the Past Fact or Fiction Fade from Memory Faerie Dreamthief Faerie Snoop Faerie Trickery Failed Conversion Failed Fording Failure // Comply Failure // Comply Fairgrounds Patrol Faith's Reward Faithful Mending Faithless Looting Falcon, Winged Wonder Falkenrath Forebear Falkenrath Gorger Fall of the Thran Fallaji Archaeologist Fallen Angel Avatar Fallen Ideal False Defeat False Demise False Memories False Mourning False Prophet False Summoning Famished Ghoul Fanatic of Rhonas Fandaniel, Telophoroi Ascian Fang, Fearless l'Cie Fang-Druid Summoner Fangkeeper's Familiar Fangren Marauder Fanning the Flames Fantastic Elasticity Far Wanderings Farid, Enterprising Salvager Farm // Market Farm // Market Fascination Fated Return Fates' Reversal Fatestitcher Fathom Fleet Swordjack Fear of Burning Alive Fear of Death Fear of Impostors Fear of Infinity Fear of Missing Out Fear of Surveillance Fearsome Awakening Feasting Troll King Feather, the Redeemed Fecundity Feed the Cycle Feeling of Dread Feldon of the Third Path Feldon's Cane Fell Gravship Fell Horseman Fell Horseman Fell Shepherd Femeref Enchantress Feral Appetite Feral Deathgorger Feral Deathgorger Fervent Denial Festering Goblin

Finally, a well-timed Fumble is a cheeky piece of tech that can turn any attack with more than one creature into a bait-and-switch scenario, letting us dodge either removal spells or pesky blocks (and sometimes both)
If youre the one playing it, its hilarious (and devastating) to ping it with damage and ruin your opponents board