#define target_height skill80
...
my.target_height = XYZ; // either some value or for example c_trace and then target.z (when trace_hit != 0) + let's say 128
my.skill81 += 8*time_step; // may be a little too fast
my.skill81 %= 360;
my.skill82 = my.target_height+32*sinv(my.skill81)*time_step; // cover a vertical distance of 2*32 = 64 quants
c_move(me,nullvector,vector(0,0,my.skill82-my.z),IGNORE_PASSABLE);