I know that we don't use the spoiler syntax in Markdown very often, but it seems it's a bit buggy, at least on this site.
Consider the following test of the spoiler tag, containing both some text and an image:
>! This is a test of the spoiler tag. >! !(https://i.stack.imgur.com/vECQ8.jpg)
This displays incorrectly, and it just registers as a normal blockquote:
This behaviour goes away if you separate the text from the image with, say, a horizontal rule, but this is hardly ideal:
It seems to me that this is buggy behaviour and ought to be fixed (and also fixable relatively easily?).