Fang attacks with very high damage, and therefore are powerful in groups. They are even more powerful with their ability Venom. However, they have very low health, and can easily be slaughtered by Booby Traps or Cannon/Laser Tower. You must either send in a group of defensive monsters such as Ichis and Crabatrons to distract towers while your Fangs wreak havoc.
Fangs may be of some use in Monster Bunkers too. With their high attack it could easily damage your opponent's monsters. Also if your Fang is at max level with max venom then it could easily damage and kill your opponent's monster even after the fang dies.
Because Fang's Venom stacks multiple Fangs attacks and the Venom lasts a very long time, they are perfect for taking out an opposing Drull/Gorgo whilst attacking. When used in a Monster Bunker, a single Fang can kill a single D.A.V.E at the cost of the Monster Bunker, which will be attacked after the Fang dies.