you can use playmaker to get/create that game object once the item should be fired.
then you need to apply
-Direction by using actions, smooth look at and move towards. THis will make it so that the missile will always look at the target so it seems like its a homing missile and it will move towards the target. You should probably check box for every frame so that its consitantly updating rotation and position.
-If you want to missile to destroy itself after x amount of time apply wait x sec and then transition to hit/no hit if no hit destroy after x time if hit apply dog
-Damage you apply int in negative value ie if you want it to hit at 20 hp do int add -20 int value apply to Gameobject health manager or whatever you call it. You can change this value for more or less.
-for speed i'm not looking at playmaker atm but im pretty sure you can adjust movement speed for the move towards as well as the look at so if you want a slower turning missile just lower and vice versa.
add particle effects and bam she-dam you got yourself a missile. Make sure that you apply the destroy gameobject after your impact/calculations as setting destroy gameobject as first action in a state will negate the remaining actions after it.
Hope that helps you.
