I'm going to critique by card type to make things more streamlined.
LANDS
Too much land, you're running 30, you don't need more than 22 lands period for a deck like this. Also
Inkmoth Nexus is what makes this deck expensive. I would sub it out for one more
forest and one more
island to make it super cheap. There are also cheap "enters the battlefield tapped" dual lands you can run for more mana variation.
Thornwood Falls come to mind So something like this.
7
Island7
Forest4
Thornwood Falls2
Simic Growth Chamber2
Rogue's PassageCREATURES
Viral drake is kind of expensive for what you get, and the mamba is pretty good so I would lose a drake and add a snake.
-1
Viral Drake+1
Blight Mamba Also we have extra slots from the lands we cut, so
Glistener Elf is a must as a 1-drop with infect. After this we'll be at 56 cards. So that's four open slots
+4
Glistener ElfENCHANTMENTS
Inexorable Tide is good, but four is too much. Just move it down to two. After this we will have 54 cards, so six open slots.
-2
Inexorable TideINSTANTS
Four mana counterspells are VERY situational with how much you have to leave open, so downing
Fuel for the Cause by two will work. In its place, add 4
Corrupted Resolve, it's cheaper and with infect the "poisoned" requirement shouldn't be hard to make. That brings us up to 56 cards.
-2
Fuel for the Cause+4
Corrupted ResolveSorceries
Overrun is a good finisher, but four is too much. In early game it can be a
dead draw and that's just a waste. Going down to two would work fine since you don't need it until mid to late game anyhow. That brings us back down to 54 cards.
-2
OverrunSUGGESTIONS
So there are SIX open slots at the end to fill out. Here are some ideas for those slots.
Elixir of Immortality- You didn't have one, every deck should have one, just one.
Tezzeret's Gambit- Drawing cards is good, proliferating is good. You can pay 2 life in a pinch to reduce the cost making it a little more versatile. I wouldn't add more than two however.
Ezuri, Claw of Progress- Strangely enough he'd be a well fit 1-of in the deck since most of the creatures have under 2 power. He'd make them larger for more poison counters.
Blight Widow- Two of these can help against flyers along with the added bonus that they fall under the Ezuri line.
That's how I would spend the six open slots, but it is in the end up to you. Hope you found this little critique helpful.