Let me show you one of my favorite decks of all time, one that qualified me for my second-ever Pro Tour in Honolulu 2006.
The PTQ format was Extended and U/G Threshold was the deck I'd played with the most. My actual list is lost somewhere in the ether of the internet. Luckily, Adam Prosak's has survived. Way back in the day, I and Adam shared ideas in mIRC as CitrusD and ihatepants. Those were the days before Magic Online decklists became readily accessible.
Blue and green. Primarily wins with a one-mana green creature. Hard to play against and punishes players with Upheaval when they tap out.
It was not so different from Infect.
One of my favorite cards in the deck was Opt. It made more hands keepable and let me react to my opponent. It fueled threshold and helped find what I was looking for. The selection let me play situational cards like Force Spike and Upheaval more easily too.
Opt is a reprint from Ixalan that hasn't been legal in Modern since its inception. Slowly and surely cheap cantrips have been banned from Modern, proving that card selection is very powerful: Ponder, Preordain, Gitaxian Probe. After the dust settled, we were left with Serum Visions, Sleight of Hand, and Peek. Opt is the first instance of another blue cantrip actually entering Modern.
How does Opt affect Infect?
Infect really does like card selection. The Legacy version runs Brainstorm, Ponder, and Sylvan Library to find its combo of "creature" plus "pump spell" plus Berserk. The Modern build rarely runs Serum Visions. It would run card selection cantrips if they were better.
Opt looks to be good enough for Infect.
The instant speed of Opt allows you to pass with a mana or an uncracked fetchland up. This dissuades opponents from casting their removal spell in the end step or from casting things in their main phases. Having an open mana up during the opponent's turn lets you leave up a protection spell, Spell Pierce, Dismember, Peek, and Opt up all at once. If Dryad Arbor is still in your deck, then that's an option too.
Opt lets you do your card selection on the opponent's turn. You can gauge if you need to find another threat or pump spell based on their turn. I imagine some opponents might be surprised at first from the Opt, think for a while, and then let it resolve. This will be a soft tell that removal is coming and that another threat is needed.
With Opt in the mix, I think Infect will undergo some reimagining. It'll want to do several things with its open mana on the end step. This means more cards "like" Opt, such as Peek and Piracy Charm. This also means an Island should (finally) make its way into the deck.
Compost really punished black removal in 2006. I'd eventually bury my opponent in card advantage. They never saw it coming.
Shapers' Sanctuary is a defensive card advantage enchantment, sort of like Compost from U/G Upheaval's sideboard. Shapers' Sanctuary will replace Wild Defiance as the card you want against the million-removal-spell decks. Only costing one mana is huge.
The problem with Wild Defiance was that you really wanted to land it before your creatures, but that meant doing close to nothing on your first few turns. Then, if your opponent isn't under pressure, they're more likely to have a counterspell or a different answer to the Wild Defiance. The Jeskai decks packing Electrolyze were the biggest reason to play Wild Defiance, but Grixis variants were also an issue.
Wild Defiance also didn't do anything against non-damage removal like Path to Exile, Terminate, Fatal Push, or Abrupt Decay, meaning it wasn't even very good against Jund or Abzan. Shapers' Sanctuary looks to be a fine card against any removal spell.
Shapers' Sanctuary also triggers off abilities targeting your creatures. This is relevant against Walking Ballista; Grim Lavamancer; Liliana, the Last Hope; or Izzet Staticaster. Sure, your creature still dies if you don't have a protection spell, but you aren't falling as far behind as before. Those great sideboard cards against Infect might actually be beatable now.
Shapers' Sanctuary is also worded where you draw twice if two of your creatures are targeted at once. This is useful against Electrolyze or Kologhan's Command Shattering an Inkmoth Nexus and Shocking something small.
It's unclear which artifact(s) you want against the heavy-graveyard decks like Dredge while also having applications against decks and cards that only slightly use the graveyard. Snapcaster Mage, Tarmogoyf, and Knight of the Reliquary are some examples of cards you'd like to nerf but don't want to commit too much toward doing so.
I've never liked Tormod's Crypt. I'd rather go ahead and pay my one mana on turn 1 and skip a possible play like Noble Hierarch or Glistener Elf in exchange for a better overall Magic card. Relic of Progenitus is good as noncommittal graveyard interaction, but can be a little slow. Grafdigger's Cage is pretty great at stopping Dredge's creatures from coming back and stopping flashback. It's also good against Collective Company and Chord of Calling.
I don't think Sentinel Totem will overtake the slots of Grafdigger's Cage or Relic of Progenitus in Infect. It doesn't quite do enough of any particular thing. Scry 1 is pretty nice, especially in a deck that combo-oriented and wants to end the game quickly, but I don't think it's quite enough.
Search for Azcanta isn't quite Sylvan Library, but it can be a good tool when you want to fight on a different axis. It's some (slow) card selection that fuels Become Immense and can out-grind the opponents stocked on removal. When it flips, it can't find a threat with its activated ability, but it can still find cantrips like Opt or Peek. Carrion Call is a spell that creates a threat and works well naturally with the game pattern that you want to be playing. You want cards like Search for Azcanta and Shapers' Sanctuary against Path to Exile decks, so hitting four mana is less of an issue.
Enough talk about possible cards. Let's get to the list!
I'm going lower on Vines of Vastwood here because you're now going to have double green less often. The Island in the deck really makes this difficult. The good news is that Infect has changed a lot over the past few years to where I don't think double green is as necessary anymore. The biggest helper in this regard is Become Immense, which does most of the job two pump spells would do for a single green mana.
Blossoming Defense is still pretty good as a small pump spell and protection spell. You need enough of this effect so that, when Vines of Vastwood becomes bad, you can fill up on the other cards. Apostle's Blessing and Spell Pierce help here too.
There are more one-mana blue spells than ever in this build of Infect. In a way, they all play well with each other. The instant-speed ones give you options on the opponent's turn. Distortion Strike (and maybe +2/-1 from Piracy Charm) makes use of the basic Island when the time comes.
Search for Azcanta, Shapers' Sanctuary, Carrion Call, and Nissa, Voice of Zendikar will likely be a package that comes in at once. Nearly every Modern deck has to respect the speed of Infect and thus tones down their mana curve in favor of cheap interaction. Once that happens, it's really tough to stick an Infect creature and you just have to hope your protection spells line up correctly. Switching gears a bit puts you in a spot where you're going over the top of what they're doing instead of the reverse.
The Dryad Arbor couldn't make it into the maindeck this time because the mana is more stressed than before. It's still a fine tool against Liliana of the Veil and Grixis Death's Shadow players that purposely put themselves really low. Dryad Arbor is less of an actual threat now with the switch from Wild Defiance to Shapers' Sanctuary. Before, you could really sneak some games with an end-step Dryad Arbor fetch if you had a Wild Defiance on the battlefield. Infect can do some cute things, but not all of the cute things all at once.
Dissenter's Deliverance and Viridian Corrupter are concessions to Chalice of the Void. Nature's Claim is still a necessity, since you want something that can remove an enchantment. Nature's Claim is also just the best card to have against Affinity, although Dissenter's Deliverance and Viridian Corrupter aren't exactly slouches.
I played Nissa, Voice of Zendikar in my Infect sideboard at SCG Richmond in August. It was a suggestion from Todd Stevens that played out surprisingly well. She's a pseudo-pump spell with her -2. The Plants preserve your life total and the planeswalker must be dealt with before the ultimate. This particular slot was reserved for Kitchen Finks before, but I didn't find Kitchen Finks significantly helping my win percentage against Burn or Jund and felt like it was just a losing battle to try.
Of course, Nissa is a deckbuilding rollover from the previous build of Infect. It could be entirely true that the shift away from wanting and needing multiple green sources could prove relevant for a sideboard card that requires double green. If that's the case, I guess I'll have to look elsewhere. Nissa, Steward of Elements zeroing to put Inkmoth Nexus on the battlefield sounds appealing…
Before, Infect was a deck with "eight to ten green fetchlands." They all got Forest, Breeding Pool, and Dryad Arbor, and the only reason to mix them up was against Pithing Needle. With Island in the deck, Misty Rainforest is way better than the rest of the green fetchlands. Try to use Misty Rainforest to get basic Island if you can afford to. Use all of the other fetchlands to get Forest or Breeding Pool.
The deck is loaded with one-ofs, something I notoriously like to do. It keeps people guessing. With Opt now in the deck, one-ofs get better since you have access to more of your deck on average each game. It does require extra ink from your pen writing down your decklists and isn't very easy on the eyes, but who cares.
Infect for Charlotte
The first SCG Tour® Modern stop with Ixalan will be a month from today in Charlotte. Depending on how many people still favor Grixis Death's Shadow will determine how well-positioned Infect is. The good news is that it looks like Death's Shadow's popularity is dwindling, while good matchups like Storm and TitanShift are picking up.
Ixalan is giving Infect a lot of new tools. Soon it might just be time for Infect to rise to the top again.