The Dragon's Fire on a Stick is a LEGO Ninjago weapon used by Kai. It is a silver staff with flames (the titular "dragon's fire") emitting from one end. According to its official description, it is an upgraded version of the Dragon's Fire, with a long handle making it safer for the user while retaining its devastating power to use against enemies.
This is a newer version of Dragon's Fire. As you know, Dragon's Fire is very volatile and the risk of getting hurt yourself, rather than injuring your enemy, was simply too great. So this version on a stick was created to improve safety for the user. It's still pretty horrible to be at the receiving end of it, though.