This RU combo/aggro deck layers several instants on top of Kiln or Nivix to win in a single strike. There are many versions of this deck, and many names for it, among which Eye Candy is one.

The most common way to stop this well known deck is to take out one of its most effective creatures, most especially Kiln Fiend. Much of the build variation relates to how to protect such creatures or somehow inflict critical damage before the creature is removed. Having experimented with a various builds, I believe that having several (or more) defensive spells (i.e. Apostle's Blessing, Pyroblast, etc.) dilutes the main punch of the deck.

Another weakness is that the pieces of the combo don't always come together. This is usually solved with deck manipulation spells (Ponder, preordain, brainstorm, gush, etc.).

My solution:

The best defense is ALSO a good offense, thus reinforcing the main theme of the deck instead of taking away from it. Therefore I dispense with stuff like Apostle's Blessing and Pyroblast in favor of things like:

Brute Force
Reckless Charge

Brute Force is obvious: +3/+3 negates the common 3 damage spell, or can provide a huge offensive boost (or in rare cases both if the removal spell is cast on my turn as I bring it out, and then follow with a Reckless charge).

Reckless Charge is less obvious but more important: Control decks will have their way with me when they have access to mana. But control is usually slow. So I can patiently wait until I have enough mana for a one turn victory. That could be as early as turn 4 if I get a Kiln Fiend combined with Reckless Charge and Assault Probe. Alternatively, if I manage to somewhat damage the opponent early on before my first creature gets removed, the second creature won't need to do a full 20 damage so Reckless charge combined with a Kiln or Nivix may be enough to end the game, in situations where the opponent has some creatures out but they are all tapped.

Lastly, though the main deck will have 12 creatures (4 Delver, 4 Nivix, 4 Fiend), I will address opponents with extremely heavy removal by having additional creatures in sideboard, primarily Elusive Spellfist, maybe one Whirlwind Adept (hexproof). I don't understand the point of countermagic as it uses up a card that could have been a creature - trading one for one. I guess if they can nail 2 creatures with one spell that would be a reason but there's not too much that does that.

As for addressing assembling the pieces: I have more access to the crucial evasion piece because of flashback on Artful Dodge and Defy Gravity. Should they end up in the graveyard for any reason (I used them once, I went up to 8 cards, opponent casts a discard or mill spell, etc.), they are part of my extended hand.

The double strike piece also becomes a little less necessary thanks to Reckless charge (which also has costly flashback). This is because I may get in a first shot for 10 damage with Reckless Charge. And then when I get a 2nd creature get in a second shot of 10 damage along with Reckless charge, though that second shot only works if I have a lot of Mana to cast the Reckless Charge from the graveyard.

The one remaining vulnerability of this deck is creatures. If I get no creatures in the opening hand, I should probably mulligan, though I might take a chance on starting hands that have everything else - Reckless Charge, Artful Dodge, Assault Strobe, and 2-3 lands (both colors). Note that Ideas Unbound partly addresses this vulnerability. If I get to turn 3 and still have no creatures, but do have Ideas Unbound, I can use one to rework the hand.

Ramblings:

I'm really liking this version. As soon as I get Delver of Secrets, I can put that in for Elusive Spellfist and Wee Dragonauts. I have yet to find WeeD helpful. Elusive is nicer because it it's cheaper and has built-in unblockability. It can draw the first removal and maybe Kiln fiend will survive after it comes out.

The only thing I really need is some way to transform my hand when I'm stalling out (no creatures, usually). Rhystic study might be a way. But I think Ideas Unbound fits better with my deck. For example, if I draw a Kiln Fiend and already have Ideas Unbound in a late part of game, I can do a draw 3 hail mary to try to get reckless charge.

Ideas Unbound is a late game card when I am low or out of cards. I want to use all my cards before the end step when forced to discard 3. I am really surprised that no Kiln fiend decks use it, so far as I've seen.

When I get hold of Ideas Unbound, I'll take out Preordain and the two Searing Blazes.