Hot on the heels of Rich’s p16, here’s a period 18 oscillator, once again found using apgsearch. It even bears a family resemblance to the p16: D2_+1 symmetry and shuttle behavior. But… it doesn’t work in Life (B3/S23). It works in B357/S23.
x = 13, y = 5, rule = B357/S23 b2ob2ob2ob2ob$o4bobo4bo$5bobo5b$4bo3bo4b$3b3ob3o3b!