Dark Star X is a character from Mario and Luigi Bowser's Inside Story and MarioMario54321's OiramOiram12345 and the Dark Star X videos, who makes a few very rare cameo appearances in Smg4's videos. The first cameo appearance was on the tv in the random guy's house in the background in 0% of spaghetti, along with Dark Fawful X and Dark Bowser X. In the same blooper MarioMario himself actually flies by riding the Dark star X while the guy is chasing smg4 and Mario. It later appeared in Join The Evil Side where MM defeated it.
- Oddly enough, even though having very few appearances in smg4's videos, Dark Star X still appears on Smg4's Facebook background sneaking up behind MM.