raginggoblin

Whispersilk cloak gives shroud, do NOT use it.

Blighted agent is unblockable and some of his creatures have evasion. Trample is not needed.

Don't use slaughterhorn, why would you even suggest that?

Never drop mutagenic growth from an infect deck. It's 0 mana for +2. That's ridiculous.

And no, you don't need a backup plan. A backup plan dilutes the deck and makes it's primary win con less likely. and of all things, you pick Adephage?

I don't mean to be rude, but your comments are trying to make the deck worse rather than better.

Overall, this deck still needs a lot of work :/
It looks like you're trying to stay on a budget, but if you really want to have a good UG Infect deck it needs to look like this:
http://www.mtgvault.com/raginggoblin/decks/modern-ug-infect/

Is this for modern or legacy?

either way you need to cut mind sculptors, merrow commerces, and merfolk of the pearl tridents. Replace aquitect's will with spreading seas.
you MUST add lord of atlantis and aether vial.

16-18 land is good for affinity.
Do you know what Cranial Plating does?
Even with the legend rule update in M14 you can still run only three Mox Opals and be fine.

stop trolling.

-2 Gaddock Teeg
+2 Tajuru Preserver

-1 Rest in Peace
-1 Grafdigger's Cage
+2 Stony Silence

http://www.mtgvault.com/raginggoblin/decks/modern-ug-infect/

That's my advice.

Whipflare is the only card in the sideboard that should be there. Those creatures aren't sideboard cards. Sideboards are designed to have specific cards that help your matchups. You should have cards like mindbreak trap, grafdigger's cage, ethersworn canonist, and disenchant. Think along the lines of what cards beat popular legacy decks when you make a sideboard.

And I agree with n3ffy that champion should be mainboarded, though mabye 2 or 3 instead of a full playset.

-2 temple garden
+2 sacred foundry
-1 forest
+1 mountain

For sideboard: replace molten rain with sowing salt.
And you only need sundering growth OR ancient grudge. You should drop one for torpor orbs.
Same goes for grafdigger's and rest in peace; you only need one.

I used to play a deck similar to this. Maybe try replacing some of the 0 cost creatures with gitaxian probe and gut shot. They both can be cast for zero as well so erayo will trigger, but they do more than just sit there.

Nova Chaser is another great red creature to use with torpor orb.

Also, try adding terminate either instead of or in addition to dreadbore.

A playset of thoughtcast is perfect. He doesn't need to change it.

standard = money trap

also, stoneforge is only 10 bucks, kind of a deal really

replace phyrexian walker with signal pest.
Also, since this is legacy, cut steelshaper's gift and add stoneforge mystic instead.

You should cut tarfire for aether vial. It's not quite as powerful as it is in the legacy version, but it really is a hugely powerful card.

replace a creeping tar pit with a celestial colonnade

Griselbrand and Blazing archon should both be here (archon in sb probs). And you can just cut your white mana altogether, you should never have enough mana to hardcast your large white creatures, you will have lost by then.
Rather than white, splash blue for brainstorm, daze, careful study, and FoW

What's the point of carrion feeder? You don't want to be sacrificing your big guys after you go through all that trouble to reanimate them.

Master Biomancer interacts poorly with undying creatures.

get excited for the new hydra!
http://forums.mtgsalvation.com/attachment.php?attachmentid=141373&d=1366039131

Orim's Chant.
You also could benefit from Enlightened tutor to help you find your scepters.

Duskmantle is pretty good (as long as we're talking about the card draw one). Replace Jace with two of them, your curve is low enough where it won't hurt you very much, and that kind of card advantage is always helpful.

Mr. Great Destroyer has no idea what he's talking about, cause Rakdos' Return is a very powerful card, and you should definitely keep your 2 mainboard.

Ultimate Price is actually a lot better than people give it credit for: it is instant speed removal that can deal with Hellrider and Restoration Angel, that's pretty good.

Reckless Walf should not be in here.

You need to up your instant/sorcery count a lot to be able to consistently flip Delver.

Overall it looks pretty good, I'd add a couple Dimir Charm and Syncopate, I'd put Ultimate Price back, and I'd replace jace with Duskmantle.