Question: During a battle between two extremely powerful space wizards, a beam of magical lightning has blasted a perfectly circular hole around 10 feet in diameter directly through an Earth-sized planet. In and out like a gunshot through paper. How would this impact life on the planet after this event, if at all?

NOTE: The incident occured about 150 miles south of the planet's north pole.

Answer: 
Depends on the side effects of the weapon.

* If a 3 m wide, 12,750 km long plug through the center of the Earth simply **disappears**, at worst there will be two smallish volcanoes and a couple of earthquakes. The total material is roughly a cube 450 m to a side.
* If sufficient force is applied to **punch** such a plug out of the Earth by conventional means like a bullet, the amount of energy that is imparted will cause major destruction.
The first thing that occurs to me is that 10 feet in diameter is very, very, very etc. insignificant compared to the total surface area of the Earth (196,900,000 square miles).

The second thing that occurs to me is the location of the event -- 150 miles south of the north pole, or latitude 87.5 degrees north. It's very likely that's in the middle of the Arctic Ocean.

So even though this magical lightning bolt has the power to go "straight" through the Earth and out the other side (somewhere in Antarctica?), I can't see it as having much actual effect, or leaving any lasting sign.

First, water would rush into the hole, rapidly cooling it.

Deeper down, pressure would cause the tube to collapse in on itself, probably almost instantly, especially since I believe you wrote that there's no debris left behind.

The lack of debris makes me think this beam is more like a disintegrator rather than a projectile -- so it's not really like a bullet at all. It's magically removing the matter from existence.

So on the way out... perhaps a highly localized atmospheric disturbance, like a thunderclap, as air rushes to replace the missing matter... but that would be that.

The hole might last a bit longer down in arid Antarctica than up in the Arctic Circle, but it would be a curiosity, little more.