Shipwreck Singer: This card draws so much hate, and it only costs 2CMC. The siren ability to force an attack is really what makes this card shine to either remove a potential blocker or get rid of those annoying utility creatures that people will not attack with, and that ability doesn't even require tapping. The -1/-1 is simply amazing against token decks. And on top of all that, a flier.
Dark Impostor: This replaced Baral. Baral is situational. Though spell casting can benefit greatly from him I don't run sufficient counters to make great use of him. Dark Impostor on the other hand, can benefit me in the long run and in the late game have an instant affect on the board state. It will draw a lot of removal yes, but if not dealt quickly becomes a very lethal asset and is an excellent counter to a re-animator type deck.
Nightscape Familiar: Cost reduction for blue on a creature that can regenerate for 2CMC. Doubles as a great chump blocker. This gets around the color requirements because it's says red and does not present the symbol. No reason not to run this, though I've never actually used it.
Courtly Provocateur: I want to remove this card because it's a 1/1 for 3CMC, but its so damn useful to remove the opponents utility creatures. I've had people waste Murder on this card, which is essentially a win for me.
Cryptoplasm: Staple creature. People say it's slow, but that's fine because it doesn't need to be fast. This card does more than just become a copy of something on your upkeep. It gives you advantage against creatures that have not yet hit the field, and many times will delay your opponents from putting out their heavy hitters or even commander because they know they'll be seeing that creature come right back at them. Its a 3CMC creature that draws removal, and if it doesn't becomes a constantly changing threat.
Dimir Doppelganger: On the chop block. This card does have its uses since it doesn't require tapping to use its ability. Excellent against graveyard recursion. But situational otherwise. Does well after hitting someone with Traumatize but I never seem to get much use out of this card.
Nightveil Specter: Early or late game, if this creature hits it quickly provides huge card advantage.
Serendib Sorcerer: Another 1/1 for 3CMC that I want to drop but just can't. This thing saves lives...mostly mine. Also great at neutralizing blockers or utility creatures.
Thassa, God of the Sea: Achieving devotion should not be hard. Scry every turn and for 2 mana make something unblockable. This replaces Guard Gomazoa, it's a great blocker against none-tramplers but that's about it.
Hostage Taker: Replacing Pull from the Deep. This has the potential to be a 3 for 1 card and fits perfectly with the deck's theme. It's a better late game drop so you can immediately cast the exiled card, but can also act as a pseudo-blink on my own creatures.
Clever Impersonator: I make a blue deck, this always goes in. It's a better Clone and doesn't target.
Evil Twin: Wouldn't be Dimir without this back stabber. Keep in mind, the ETB effect doesn't target. Only downside to this creature is that it requires tapping to kill, but then if it didnt it would be OP'd.
Stunt Double: Replacing Diluvian Primordial, I like Diluvian because it's a potent flying threat but does cost 7CMC; he might get put back in. Stunt Double adds a nice flare to my deck, flashing in at opportune times to catch an opponent off guard.
Gonti, Lord of Luxury: Card advantage + DT blocker. Haven't used him yet but I am very anxious to.
Consuming Aberration: EHD multiplayer and I'm using minor mill, why wouldn't this be included? This wins games, simple as that and adds more fuel in the graveyard.
Havengul Lich: Still have yet to use this, but its value is obvious. Grave robbing at the additional cost of 1 mana of any color.
Mulldrifter: So this is either Divination early on or for 2 more mana that plus a 2/2 flier. No draw backs here. Deep Analysis could be substituted here for an additional 2-card draw though I'm not sure if I'll need the potential blocker or not.
Stitcher Geralf: I have considered removing this many times, but Geralf typically leads to a game winning move when he's out, even better when Lazav is out because I can choose what hits the graveyard then. Additionally he can deny grave-diggers of the creatures they need with the exile clause.
The Scarab God: This was added for the obvious synergy of minor-mill conditions in the deck, but it was difficult to remove Willbreaker to make room for him.
AEtherling: Staple blue creature that is nearly impossible to get rid of so long as I have mana to spend. Game winner.
Arcanis the Omnipotent: Great draw engine that can survive wipes or block and save itself.
Keiga, the Tide Star: So 5/5 flier for 6CMC, good. On death effect, brutal. If opponent has a large threat out, keep Keiga as a blocker and they'll never attack. Attack with Keiga and either they take 5 or lose a chump blocker. Normally this card will draw a prison or exile effect. Combo's extremely well with copy mechanisms using the Legends rule. I want to so badly kick Rite onto this guy.
Sphinx of Magosi: 6/6 flier for 6CMC is already very good, but I also get a card draw engine with Hydra-potential for a non-tapping 3CMC ability.
Steel Hellkite: Like above, 5/5 flier for 6CMC is good. Now give it fire-breathing and permanent destruction. This is a great card that draws a lot of hate and for good reason. Doesnt combo well with my deck though.
Wrexial, the Risen Deep: This is my replacement commander if I find Lazav lacking. 5/8 for 6CMC is ridiculous, now look at everything else.
Chancellor of the Spires: One of the few cards in my deck that can go Infinite with the right card in an opponent's graveyard. The beauty is that after the spell is casted it doesnt get exiled like with Wrexial and Primordial. 5/7 Flier on top of it, excellent. Opening hand mill is also fun, only had that happen once though. Excellent target for token generation
Phyrexian Ingester: Blue fatty removal in exile form, delicious. Good target for token production as well and bounce effects.
Sphinx of Uthuun: So, what we have here is 4CMC for Fact or Fiction at Sorcery speed, and then a 5/6 Flier for 3CMC.
Stormtide Leviathan: If I had a win condition it's this. Put it out and start wrecking. Clone it for additional fun to be had by me. Kick Rite onto it or attach Infinite Reflexion: two of the many ways to abuse this card.