I built a ghast farm. It took a long time. Ghasts seem to be bugged with lag when firing, and even when just existing.

To replicate the bug, build a containment unit for ghasts in minecarts. Then, get them to fire at you. If multiple fireballs are in the air at the same time, or if the fireballs are redirected with slime, they cause a lag spike that slows entities in motion, such as minecarts, boats, arrows, fireballs. It should also mess up the day/night cycle, and after stoping the ghast firing, there will still be significant amounts of lag that can make building frustrating.

To stop the world from lagging, you can either unload the chunks, or reload the world. But as soon as they fire again you should notice the bugs described above.

As an added note, my world is around 500 MB, not sure if the world size effects this bug though.