Spiky Ball

Thrown at something, one drops almost straight down and lands short, so aiming is close to pointless. These are meant to be scattered where the fight is about to happen. Anything that walks over the pile takes hit after hit until each ball is used up, and a ball that nothing touches only sits there for a bit over a minute before it disappears. That is long enough to prepare for a fight and short enough that you cannot lay the floor the night before. Auto-reuse means holding the button carpets a stretch of ground in a second or two.

Anything that fights at floor level. King Slime, the Eater of Worlds and the Brain of Cthulhu all come down to your height, and a layer laid in advance grinds them down while you concentrate on dodging. Against anything without knockback resistance the pile doubles as a wall: each hit shoves the enemy back onto the next ball, and it never reaches you. They will not fall through platforms either, so a raised deck holds a layer and you can fight from under it.

• They cannot hurt you and they ignore town NPCs, but they do damage other players, which comes up in multiplayer more often than you would think.
• Once one leaves your hand it is gone. There is no picking it back up.
• Thrown against a slope, a ball rides up the slope instead of bouncing off it.
• With frost armor equipped the frostbite glow turns a scattered pile into cheap lighting.

A Goblin Army hands these out in absurd numbers, which sets up the obvious joke: the best counter to a goblin invasion is the last goblin invasion. Lay a layer the moment you have them, because that event is nothing but grounded enemies walking at you in a line. The Goblin Tinkerer sells them too, and he throws them himself when something gets close to his house. Whatever you do not scatter sells for enough that a full stack is real money early in a world.