A solution for FCG could be found in a minimal red splash for a card that is most certainly bad but would solve the problem at hand and be strong against the other fish variants:

Fire Covenant
Instant
1RB
Pay X life: Fire Covenant deals X damage divided as you chose among any number of target creatures.

The mana cost is extremely low, probably the most efficiently-costed one-sided mass destruction in the game. Red would be easy to splash via bloodstained mires and badlands. This obviously either ties up a large portion of the board or makes you vulnerable to wasteland, so its a matter of compromise and metagame. Of import is that the paying of life is not a part of the casting cost and so any pumps to a mongrel would have to be done prior to such paying, unless I am reading a bad text of the card.

Edit: Incidentally, a red splash could also give access to some artifact destruction; rack and ruin or keldon vandals comes to mind. This is almost certainly taking the deck in a bad direction by adding a significant second color, but it is at least worth considering.

Bone Shredder does not off a mongrel, as they just discard a card and change the mongrel's color to black. Slay would be an option in this matchup but fails for the same reason. Faceless Butcher is almost definately too slow. Duplicant is WAY too slow, Nekrataal is too slow AND can't kill a mongrel. Those are the CIP destroy creatures. Only faceless butcher seems even remotely playable, as he removes anything and can even get creatures like Darksteel Colossus. It would be funny to beat an unsuspecting gifts.dec player with a vial on 4 when he tried to double Time Walk and beat.

The answer seems to be either Smother or Devour In Shadow. Either will kill a mongrel or a welder; smother is easier to cast and doesnt hurt you, while devour in shadow is more flexible with the ability to kill cards like platinum angel. Obviously against a mongrel the devour in shadow could end up costing you a significant amount of life, but the increased flexibility leads me to suspect that it is better than smother.

Oddly, Pithing Needle also seems to be a decent and flexible answer to the mongrel. It isn't so scary as a pure grizzly bear.

Comparing this card and Null Rod is unfair and inaccurate. Against Slaver, Null Rod can in many cases be welded away. Since this card can and probably should be naming Goblin Welder against Slaver, that is not an option. Further, Null Rod turns off artifacts, while this card can turn off ANYTHING. For example, against Dragon, you could turn off Bazaar with the first and Compulsion with the second. Its versatility is one of its strengths.

It also costs only 1, half of what Null Rod costs. In a tempo-based deck like Fish, this is certain to be a very powerful weapon. Certainly most decks are equiped to get rid of it, and by no means is it a permanent answer, but neither is Null Rod. It takes just as much time to answer this as it would to answer Null Rod, in some cases more time since this can turn off Goblin Welder (seriously, it TURNS OFF WELDER, in what way is it not an amazing card?), and at half the price it seems that in that time it generates twice the tempo that Null Rod would.

It has a tempo advantage over Null Rod, and a versatility advantage over Null Rod. The Rod is a stronger card, but versatility and tempo have many times before made up for a deficiency in power. Pithing Needle could easily become the poster card for versatility and tempo in this format.

1
Artifact
When Pithing Needle comes into play, name a card.
Activated abilities of the named card can't be played unless they're mana abilities.

This card is so incredibly versatile. It turns off something in every deck. Goblin Welder, Aether Vial, Sensei's Divining Top, Bazaar of Baghdad, just to name a few. This is the type of card that it seems should have immediate maindeck impact on the environment. Its laughable when R&D prints an answer for Jitte and Top in Block and ends up with a card that is this powerful. And its not legendary, as it should've been to stay in flavor in the Kamigawa block. And it works on lands.

1 bloodstained mire
3 wooded foothills
1 forest
1 mountain
4 taiga
3 bayou
4 mishra's workshop
8 solocryptmoxen
1 mana vault

has tested to give timely access to the needed colored sources with 2 solemn; however it has neither ancient tomb nor wasteland/stripmine, which could make it suboptimal. i just cant see a configuration with more colorless sources allowing for smooth acess to black while retaining any number of basics and giving access to sufficient green and a mountain for anger.

my configuration for the rest of the maindeck:
4 juggernaut
2 triskelion
1 razormane masticore
1 squee, goblin nabob
1 anger
4 goblin welder
1 platinum angel
1 gorilla shaman
2 solemn simulacrum
1 goblin sharpshooter
1 karn, silver golem

1 demonic tutor
3 chains of mephistopheles
2 pyrostatic pillar
4 chalice of the void
1 trinisphere
4 survival of the fittest

we can talk about what we feel is a suboptimal combo deck and what isnt, but all of that remains theory and personal preference. my goal in asking this question was to see if we could determine a quantifiable quality in combo decks that could measure the benefits of disruption and compare it to their detriments.

here is what i propose that we try to find (i would have done this in the initial post but i had to go to class):
1. is there some specific percentage of first turn goldfish wins that would make a total lack of maindeck disruption acceptable? (it has been proposed that SX goldfishes at something around 70%, depending who you ask, and clearly this isnt high enough based on the results).
2. if that statistic got high enough, could you validate a list that also lacked any sideboard disruption, i.e. is there a point at which a deck is fast enough that it invalidates the sideboard by being so effective?
3. what factors other than speed* should be used in determining the level of disruption a deck should run (for example, stability of the win condition. a deck with 4 mind's desires prior to restriction obviously could have run less disruption due to the inherent "safety" of desire, since it can't be countered except by stifle).

*for sake of uniformity, im going to losely define speed as a function of the percent of 1st turn goldfish wins a deck can post.

Recently a new combo deck has made its pressence known in the format, not through good performance but instead through a sort of notoriety that it has gained in its short lifespan. The deck is called "Meandeck Tendrils" and is a creation of the good folks at team meandeck. In this forum, it has been dubbed "Spoiled Tendrils," clearly an ironic jab at its poor performance at both Waterbury and the most recent SCG. Though this deck may not be a force in the metagame right now, it does raise an interesting question, and it is this question exactly that i pose:
Is maindeck disruption in the form of force of will, duress, or even unmask in tendrils combo worth the necessary drop in speed that results from its inclusion?
or the converse:
Is streamlined speed in tendrils combo worth the necessary exclusion of maindeck disruption?

for reference, some decklists:

Meandeck Tendrils SX
4 Tendrils of Agony
4 Spoils of the Vault
4 Night's Whisper
4 Sleight of Hand
4 Brainstorm
4 Chromatic Sphere
4 Darkwater Egg
4 Dark Ritual
4 Cabal Ritual
4 Land Grant
1 Ancestral Recall
1 Hurkyl's Recall
1 Chain of Vapor
1 Yawgmoth's Will
1 Demonic Tutor
1 Demonic Consultation
1 Lion's Eye Diamond
1 Black Lotus
1 Mox Sapphire
1 Mox Jet
1 Mox Emerald
1 Mox Pearl
1 Mox Ruby
1 Mana Crypt
1 Sol Ring
1 Mana Vault
1 Lotus Petal
1 Bayou
1 Tropical Island
1 Polluted Delta

Sideboard:
2 Chain of Vapor
2 Hurkyl's Recall
4 Force of Will
1 Bayou
3 Tormod's Crypt
1 Black Vise
1 Necropotence
1 Chrome Mox

TPS (Waterbury 3rd place list)
3 Island
2 Swamp
2 Underground Sea
1 Tolarian Academy
2 Flooded Strand
4 Polluted Delta
1 Black Lotus
1 Mox Emerald
1 Mox Jet
1 Mox Pearl
1 Mox Ruby
1 Mox Sapphire
1 Mana Crypt
1 Lotus Petal
1 Mana Vault
1 Sol Ring
1 Ancestral Recall
4 Brainstorm
1 Mystical Tutor
1 Time Walk
1 Timetwister
1 Frantic Search
2 Rebuild
1 Tinker
1 Cunning Wish
1 Gifts Ungiven
4 Force of Will
1 Time Spiral
1 Mind's Desire
4 Dark Ritual
1 Vampiric Tutor
4 Duress
1 Demonic Tutor
1 Yawgmoth's Will
1 Necropotence
2 Tendrils of Agony
1 Yawgmoth's Bargain
1 Memory Jar

Sideboard:
1 Darksteel Colossus
1 Hydroblast
1 Chain of Vapor
1 Stifle
1 Hurkyll's Recall
1 Brain Freeze
1 Echoing Truth
2 Energy Flux
1 Rushing River
1 Misdirection
2 Engineered Plague
2 Skeletal Scrying