A blast line is a boundary on a stage that a character cannot cross without getting KO'd. Some stages have blast lines that are accessible by simply walking into them such as Mushroom Kingdom II in SSF, or Skull Fortress in SSF2. Other stages have large blast lines due to their large area such as Temple.
There are four blast lines, usually referred to as "bottom"/"lower", "left", "right", and "upper"/"higher" (alternatively, "north"/"south"/"east"/"west"). The bottom blast line can also be referred as the "pit" and the upper blast line can also be referred as the "ceiling." Characters KO'd via the upper blast line are either Star KO'd or Screen KO'd.
- Prior to v0.8a, the characters KO'd via the upper blast line are not neither Star KO'd or Screen KO'd, they would be KO'ed in the same way as left/right and bottom.
- In the original Super Smash Flash, the upper blast lines of all stages except for Peach's Castle could be crossed merely by jumping high enough, making aerial camping with characters that have multiple jumps such as Kirby, Meta Knight, and Tails a dangerous and self-destructive option. This was fixed in SSF2, where crossing the upper blast line without being attacked will do nothing, as it is in all official games from Melee onward.