Bill Blasters return once again as hazards in Smash Run. They fire Bullet Bills as well as other enemies like Koopa Troopas and Shy Guys, albeit uncommonly.
Usually a big cannon with a skull on it is a clear sign that it's time to flee. Running away isn't an option in the Super Mario series, though. It may be known as the Bill Blaster, but it can occasionally fire Koopas or Shy Guys instead. Take it out before it's out of ammo for more goodies!