Maybe even another Skittles?

I would suggest at least taking out the Phyrexian Arena for another creature, one just doesn't cut it.

Love the deck +1 I use a very similar deck at my LGS and always get top 1-8 my differences are Victim of Night over Smother No SKITTLES ( vatmother #4) I often get stuck on 3-4 lands I also do not use Lilly as she is really just win more lol but she is good I prefer 27 spells for pike opposed to 24 Blackmail is really good and doesn't hurt like Thoughtseize but that is a matter of preference i guess.and about your milera-pod match up that is a match that I believe favors Infect hardest match for me is always jund. A card i have been testing is a 1of Cathedral of War the exalted trigger is very helpful for inkmoth nexus especialy if you want to give it +2 with Funeral Charm now it swings 4/1 flying infect or makes vatmother a 2 swing win. anyway good luck with the deck

Have you thought about Waste Not and Dark Ritual ? It can make for a nasty turn one. or even a turn 3 infect beater. Another win condition could be a blitterblossom as a one of or two of. and I may up the Thoughtsieze count. It just does a bit better drawing it over not drawing it. Great deck! I really like it+1 from me

Another creature buff you could test is vampires bite it is basically a black giant growth with the added benefit of lifelink if needed

Hey i played a simillar list at a modern event (I went 1-2) and Id like to make a few suggestions based on how i did. I needed more removal than the 2 Devour Flesh and 2 Slaughter Pact that I boarded. I decided to drop Funeral Charm and add in a playset of Smallpox and they overperformed quite a bit. My first round was tribal goblins and smallpox won me the game in game one. Game 2 I was down to one life and I played a Phyrexian Crusader and built enough boardstate to win me the game. Second round I played the rock with Phyrexian Obliterator and That card screwed me... I thoughtsiezed one away game one however he just drew more and that was that. smallpox kept me in the game and I had a bunch of very profitable 1 for 1 trades early but not enough hand disruption as opposed to discard ended me. round 3 hadd me against the modern event deck which was very powerful... we are helpless against the spirits as we dont have access to any boardwipes. Here are my suggestions based on my performance. Add Smallpox mainboard, and more spot removal. Also add a second urbog and drop a lilianna. I will post more updates and a link to my list once i put it up

I have a mono-black infect too and I can suggest you Mutilate and Lashwrithe (take a look on Where is your god now?, but I was wondering about how to increase the effectivenes of this deck and it should be green, so I can put a few more buffs and destroy things that black cannot! Take a look on Infect new generation and give ur feedback if possible. Good deck btw, +1!

Vampire's Bite is probably the best black buff spell in modern.

I would play 4x Lashwrithe. I do that on my MB infect and it is amazing

+1 from me.

Surgical Extraction can be used as a GY hate, so no need for Relic of Progenitus. I strongly recommend one Spellskite or two, it is mandatory in almost every deck! I do recommend some mass removal, like Damnation, Languish or Mutilate, the meta now will be super fast (zoo, affinity and tokens).

Phyrexian Arena is a very strong card on grindy games, but I took it out for the Night's Whisper effect. Btw, I would cut the draw effect, more removal/discard/pumps on this agressive meta. Overall, I like of your build. I strongly suggest more pump effects, instants or equips, they help out to close the game faster :)