Splinterling

It does not spawn in the world at all. The Pumpkin Moon has to be running, which means summoning the event yourself at nightfall in a hardmode world with Plantera already dead, and even then the first wave passes without one. From the second wave onward they arrive constantly and in numbers, and everything stops when the sun comes up.

Two enemies in the game hand over Spooky Wood, and this is the one that shows up by the dozen. Mourning Wood is slower to reach and slower to kill, so almost every plank a player owns came off these instead. If you want the spooky armor or the furniture, run more moons rather than hunting the big tree.

Kills push the wave counter along nicely on their own, faster on the higher difficulties, so a good event snowballs partly on the back of these. The banner is the one thing that takes real commitment: it wants roughly three times the usual number of kills, so it will not drop in a single night however well the run goes. The wood payout per kill was cut when the numbers went up, which is a fair trade once you see how many appear late in an event.