Smiley Bomb (スマイリー・ボム) is the fourth and final boss in Sonic Labyrinth, awaiting Sonic at the bottom of a long, Ring-filled slope in Act 4 of Labyrinth of the Castle.
Dodge the shower of tiny Eggman bombs that rain down from above at the start, and then the Smiley Bomb appears. The Smiley hovers around overhead and attacks by flying over Sonic's position and dropping a bomb. Immediately following the explosive drop, the Smiley lowers down to attack head-on at the point of impact: this is the only opportunity to attack. After 10 hits, the bottom half of the bomb disappears leaving only the creepy grinning head floating around in the air. The head attacks in the same general pattern, except rather than dropping a bomb, it vomits up a laser blast that splits into two smaller charges upon hitting the ground. Land 10 more hits on the head (total of 20) to pop the Smiley Bomb.
The boss relinquishes the blue Chaos Emerald upon being destroyed, which the player must grab to finish the game. In the ensuing end sequence. Dr. Eggman runs away, dropping the green Chaos Emerald. Collecting the gem, Sonic turns away from Eggman's escape route and instead exits the labyrinth he has been forced to take part in, the credits rolling as the hedgehog is able to run freely once again.