Graphics 16 and 17, a spider (both show the same sprite), enter here and flip their picture every turn as they go; graphics 80 and 81, a creature that falls from the sky (SKY_DROP), enter at SKY_ROAMER, which skips the flip. Either is deadly both ways (MAKE_DEADLY), and falls, faster each turn since its steps are never cleared, but never lower than 129: below that it is put back at 129 with no fall.

It runs straight at four units a turn until it bumps into something, which the collision code shows by clearing the step. Then it picks a new way, the sign from bit 3 of R: along U if the bump was in V, otherwise along V. The way it faces goes with the way it runs: bit 0 of the graphic and the mirror bit (6) of the flags make four facings from two pictures.