…Or at least a lot of them do, anyway. spikeCount="2", spikeCount="6", and spikeCount="10" all work as expected, but no odd number works properly and many even numbers result in having their results halved — spikeCount="8" results in four spikes, for example. This was specifically tested on diffraction (which yields the aforementioned incorrect results) and lightning (which works correctly, even with odd numbers). Other styles might be affected differently.

 Also, spikeCount="0" should be a valid means of removing the spikes altogether. It currently isn’t, which might be related to the above. (Something like spikeCount="0" on the lightning doesn’t make any sense, sure, but that should be the modder’s problem if they really want to do it.)

george moromisato 12 May 2021:

Fixed in 1.9 Beta 4.

The number of spikes must be an even number (because of how we paint). But other than that, I've made the changes above, including allowing "0".