More coordinates, weirder shape. A face from another world appears, point by point. Same skill as the T-Rex, but with extra eyes.
Each point (x, y) maps to (−x, y). Distances and angles stay the same — only the handedness flips.
Mirror coordinates do half the work
Give the alien a symmetric face and you only have to plot one side. If the left eye is at (3, 5), the right eye is at (−3, 5) — flip the sign of x and you've reflected across the vertical axis. Plot the left half, mirror every point, done.
Extra eyes, antennae, fangs: as long as the mask is left-right symmetric, each feature you place at (x, y) gets a free twin at (−x, y). You're drawing with reflection symmetry whether you mean to or not.
The alien's left fang tip is at (4, −6). Where is the right fang tip on a left-right symmetric face?
Symmetric features like eyes use mirror coordinates: if (3, 5) is the left eye, (−3, 5) is the right. You're drawing with reflection symmetry.