Sewers Under Kasprah – Blue Plunge & Black Flush

Plunge is a control-style mechanic that allows you to slowly mill (sort of) your opponent, while giving you the possibility of powerful scrying.

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Eyesore is a simple ETB Plunge trigger. Sanity Leech is repeatable, and being an early defender, it is invaluable to control players looking to stack their deck. Mind Scavenge is a simple instant with Plunge, which has the variability of being better, worse, or equal to Opt. Brain Feeder offers an activated Plunge ability, though I think of it as a tad expensive (for a common, it's important for it to be a little expensive). Brain Suckle essentially lets you "mill" three cards, but you also get your choice of exiling the card with the highest CMC for you to Plunge with.

Juvenile Feeder can provide an interesting choice for an opponent. Many times, and opponent who needs to decide blocks may let a simple one damage go through to block other threats, but with the triggered Plunge, the opponent may decide blocking that one damage is important. Undertow Lurker is an Instant/Sorcery payoff, which is naturally Izzet's subtheme. I may change that to be more interesting as I redesign the set. Three-Eyed Mole is a Plunge payoff, letting you constantly draw cards if you have the mana to recast Three-Eyed Mole. Pieces of Sanity is a rare enchantment that gives you a lot of inevitability. Novel Futures is a Scry payoff, but just the same way that all lifegain payoffs are also Drain payoffs, this Scry payoff is also a Plunge payoff.

Flush being a fairly simple mechanic, there won't be too much to talk about on each of these black cards.

Here, Black gets an instant, a sorcery, an enchantment, and a creature at common each with Flush. The ease of which they enter the graveyard determines their flush cost, so a cheap sorcery like Smokebomb is expensive to Flush, while permanents are a little cheaper.

The uncommons and rares get more interesting. Agonized Survivor makes you discard a card to cast, but you get a replacement after you Flush it. Rabid Blood Rebel let you sacrifice itself to act as removal, and also get it more quickly into the graveyard for Flushing. Slimesucker is a simple payoff for Flushing your cards. Rotting Feasts is a more interesting payoff for Flush, in that it turns your Flushing into removal. As well, your opponent hasn't seen the last of Rotting Feasts when they remove it, because you can activate it one last time from your graveyard. They language is a little tricky here, because as an enchantment it only works on other cards while it's on the battlefield, but it works on itself from the graveyard. I wonder if there's a way to clarify that.