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Nothing summons these. They come with the weather: while a sandstorm is blowing over a desert they roll in on their own, and they stop arriving once it passes. The event can land on a character in the first hours of a world, which is when it does the most harm. They also vanish once the nearest player is out of the desert, so retreating a screen or two onto normal ground clears the lot.

Direction is the whole fight. Rolling with the storm one moves faster than an early character can run, and in that visibility you get about half a second of warning. Rolling against it, it crawls. Jump over one, force it to turn around, and you have cut its speed for free. There is no ranged attack, so every point of damage it deals comes from touching you.

Knockback sticks, which is rare for something this quick, so a fast bow keeps one pinned at range. Arrows that leave a debuff behind earn their cost, since you tend to land glancing shots as it rolls past rather than a clean line.