Bob-ombs, known in Japan as Bomuhei (ボム兵, lit: Bomb Soldiers) are walking living bomb enemies that have appeared all long the Mario series. They originally first appeared in the non-Mario game Yume Kōjō: Doki Doki Panic, but was introduced as a Mario character in the western localization for said game, Super Mario Bros. 2. They have two white eyes, a fuse, two legs, and usually have a wind-up mechanism on their backs but is not necessary.
In Super Smash Flash
Bob-ombs appear alongside normal items in Super Smash Flash. If the player press attack near a Bob-omb, the player can pick it up, and press the attack button again to throw. When thrown, it has huge knockback, and causes 34% damage. Because of SSF's damage set and physics, a glitch that cause more than 1000% of damage may occur if a player throws a Bob-omb at a chain of, either, other Bob-ombs or activated Motion-Sensor Bombs with another player standing on them without knocking-out him.
In Super Smash Flash 2
In Super Smash Flash 2, they appear as dangerous items that are picked up and thrown (they have a small yet powerful explosion on contact). Unlike SSF, if they are left alone for too long, however, they light their own fuse and start walking around, blowing up when someone touches them (either directly or indirectly) or after a 15 seconds pass. Attacking or hitting the Bob-omb makes it explode instantly so players must be careful. It can do up to 27% damage.