Well, that's not entirely true. But despite all the careful attention I paid to the new cards from Dragons of Tarkir, I failed to recognize that the addition of just three cards into the format unleashed not one but two potentially viable "infinite" combos onto the metagame. It wasn't until I saw this post by rremedio1 that I understood what I had overlooked.
Both combos are remarkably similar, relying upon a zero cost spell plus a creature than untaps when a certain requirement is met:
For this first combo, you cast the Helix on the Zephyr Scribe, then use the newly granted ability to bounce the Net back into your hand. Then, you cast the Spidersilk Net again for free. Since this is a noncreature spell, it activates the untap secondary ability on the Scribe, untapping it. You can then repeat this indefinitely (assuming your opponent doesn't interact to stop you).
To take advantage of this interaction, all you need is something that generates an effect as often as a noncreature spell is cast. Any Prowess creature will do the trick, but Elusive Spellfist is particularly effective, since it cannot be blocked. You simply repeat the combo until the creature has enough Power to deal lethal damage and then attack with it.
The second combo also utilizes Retraction Helix, but relies upon a different creature with an untap ability. Midnight Guard untaps whenever another creature enters the battlefield. So you use the Helix to bounce the Ornithopter, then replay it for free. Since this is a creature, it triggers the untap ability of the Midnight Guard, untapping it to allow you to again repeat this as many times as you want.
To take advantage of this interaction, you need something that generates an effect whenever a creature enters the battlefield. In this case, Impact Tremors fits the bill, since it deals one damage whenever a creature enters the battlefield under your control. Repeat the combo as many times as it takes to deal lethal damage to your opponent.
Next time, I'll talk more about these two combinations and what you can do to combat them.