It tends to depict Pichu rather than Pikachu. But I note that Pichu’s electric attacks damage itself, at least in Super Smash Bros (and I find a quote from the Bulbapedia article saying “it cannot discharge without being shocked itself”), which caused a friend to refer to Pichu as “emo Pikachu”. Perhaps “goth Pikachu” ended up referring to the same thing...
It tends to depict Pichu rather than Pikachu. But I note that Pichu’s electric attacks damage itself, at least in Super Smash Bros (and I find a quote from the Bulbapedia article saying “it cannot discharge without being shocked itself”), which caused a friend to refer to Pichu as “emo Pikachu”. Perhaps “goth Pikachu” ended up referring to the same thing...