1: Kiln Fiend is the main beater of the deck. He’s usually good for a turn three win, but watch out! He only buffs his power, unlike the other creatures in the deck, so he can still be bolted.
2: Monastery Swiftspear is the backup beater, which also allows you to win a turn early with the right hand.
3: Soul-Scar Mage is just there because it's the best one drop prowess creature besides swiftspear. The wither effect is irrelevant, except maybe to Gut Shot away a single damage in Infect matchups.
3: Apostle's Blessing is extremely good. Of course it protects your creatures, but it also doesn't take up any specific mana, and it can be used as an uncanny dodge when the opponent only has one blocker.
4: Aphotic Wisps is basically me giving in to the fact that the jund matchup is an auto-lose. Since we don't care about jund, and affinity has fallen off, this is basically a Slip Through Space. In very specific situations, it can be used with apostles blessing to make the creature totally unblockable. This is an extremely efficient card, and the draw will usually give you more access to damage.
5: Assault Strobe/Temur Battle Rage are the main wincons. Note that with kiln fiend, when you play battle rage, fiend’s trigger happens before battle rage checks for ferocity, meaning fiend will get trample even if rage is the only spell you’ve cast so far.
6: Tainted Strike is rigged in this deck, and makes it way more consistent in the T2/T3 kill. It’s also where the deck got its name.
7: Manamorphose/Gut Shot/Mutagenic Growth grow your creatures for free, and make when turn two kill much easier.
8: This deck used to only play two cards which when combined would allow for a turn 2/3 kill, which were tainted strike and assault strobe (Temur battle rage was added later). The new Scale Up allows for the same thing. With kiln fiend, you can play scale up with either tainted strike or assault strobe and swing for the win. Unfortunately, if you are going for the turn two kill, scale up gives you either nine Infect or sixteen damage, unless you have a Gut Shot, Mutagenic Growth, or Manamorphose.