Gen III and IV only seem to shy-hyphenate compound words; I determined
whether or not to use a shy hyphen by looking at other instances of the
word. If it's consistently not hyphenated or just hyphenated on a line
break, I figure they mean for it to be a compound word, e.g.
"kindhearted" rather than "kind-hearted".
"Supereffective" is weird, but they seem to consistently spell it as all
one word when it's an attributive adjective, only ever hyphenating it on
a line break and only spacing it as a predicative adjective. So I
counted it as a compound word in the flavour text for Filter and Solid
Rock.
Gen II move flavour sometimes has shy hyphens; these, like in the
Pokémon flavour text, are represented by U+00AD SHY HYPHEN even though
the Unicode standard specifies that it be used to mark where a shy
hyphen *could* go rather than where one was placed. (Supposedly, at
least; I haven't read it for myself.)