The Dangerous Bomb, as the name implies, is a bomb that will make it explode in a specific radius. The blast radius has been larger in some games. It's considered dangerous, because it has a large and unusual blast radius compared to most bombs. The effect of this bomb depends on how it's used.
When two bombs collide with each other via kicking, they form a Dangerous Bomb. The most notable way of creating a Dangerous Bomb is used when a player kicks two Rubber Bombs in the same direction, in which one will bounce back to the opposite direction when hitting the wall, which will collide and form a Dangerous Bomb.
The best use of this bomb is that it can clear soft blocks around it. However, caution needs to be taken upon the blast it produces. If one is on the 5x5 square, the player will likely be eliminated. The dangerous bomb can appear so suddenly that it can catch players off guard. In some games you can grab an item that allows you to use dangerous bombs at will. If a player is surrounded by soft blocks you can use this bomb to block them in for an easy kill. However, one should note that Shields cannot be used to protect against it.
In Bomberman DS, while two bombs crash or and King Bomb-like enemy transforms, it will be a different colored bomb.
Bomberman DS: Danger Bombs in Revenge Mode
With the Revenge Mode enabled in Bomberman DS, defeated players can throw Dangerous Bombs onto the map by blowing into the microphone. Unfortunately, they just have an 3x3 explosion.