Blocker is a period-8 oscillator found by Robert Wainwright. It is a useful dot sparker consisting of two blocks hassling an unnamed object which is a dying spark. It reappears half way through its cycle rotated through 180 degrees.
Blockers can also be infinitely connected by "sharing" blocks, as long as adjacent reactions are no more than one phase apart. They can also be connected with Coe's p8, which uses blocks as hasslers in a similar manner.
Blocker is about the sixteenth most common naturally-occurring oscillator in Achim Flammenkamp's census, being less common than mazing but more common than jam. On Catagolue, it is the second most common period 8 oscillator, being less common than the figure eight but more common than Coe's p8.
The first natural blocker stator variant, blocker on cap, occurred in September 2015.
- 15P8.1 at Heinrich Koenig's Game of Life Object Catalogs