You just aim and click. The only time it is effective is when it goes into the dragon's mouth when there are no flames there (you have to put it to sleep for a second or two). Climb around the back, Dodge the spike ball, and pull the lever.
(see related question)
To shoot the ice arrow on Astro Knights Island in Poptropica, you need to equip the bow and arrow from the armory in the castle. Aim the bow at the ice shard above the dragon's mouth and release the arrow by clicking or tapping on the screen. This will break the ice shard, allowing you to proceed in the game.
You shoot the arrow at the tower to the left then jump on the rope and go in the tower. hope this helps!!
The crossbow will let you create a way into the Princess tower. Get the rope from the water wheel at the mill and tie it to an arrow. Aim up to the left and shoot until you hit the door.
on astro-knights.
There are no fish on Astro Knights Island. There are Space Sharks around the Ice Planet at X-73 Y-83. To defeat them, shoot them and lure them to the Black Hole at X-85 Y-47. (see related question)
Dodge them or shoot -- click your mouse to shoot, and watch out for pieces. (If you take a Space Shark to the Asteroids, he swims right through them!)
To reach the left-side tower of the castle (the Princess room), you need to use the rope from the Mill. Tie it to the arrow on the giant crossbow and shoot it left and up to hit the tower door. (You get many tries.)
You shoot them
get the rope from the wodden thing in the mud next to the mill, then put the rope on the arrow, and shoot it towards the castle.
*You can only use the Ice Arrow when the dragon is "asleep" for a few seconds, with its eyes closed and mouth open. You create this by climbing OVER the dragon to the back, then slipping past the spike tail to flip the lever on its back. VERY QUICKLY jump back in front of the dragon and shoot an Ice Arrow into its open mouth. (You have to do this whole process three times.) To shoot the Ice Arrow, click on the icon at the lower left, and aim for its mouth, then click again to shoot.
Go behind the monster, climb on its back, pull the switch, then go in front of the monster and shoot the ice arrow into its mouth. Do this 3 times and you will defeat the monster.(see the related solution)
It is on the outside ramparts of the castle. Get the rope on the wheel beside the windmill, and tie it to one of the big arrows. Shoot up and left to hit the door in the disconnected Princess tower. (You get more than one shot.)
You have to move fast once you throw the lever on the dragon's back. You only have 5-10 seconds, and missing more than once will probably force you to reset and try again.