To make it kill on impact, in the players code you should put:

That would randomly move the character right

Actor actor = getOneIntersectingObject(enemy.class); if(actor != null) this part checks if there is an object from the enemy class getWorld().removeObject(this); this will remove the character if it has been touched by the object from the enemy class

Greenfoot.getRandomNumber(5) will choose a random number between 0 and 4, the ==0 will check if the random number is equal to 0. setLocation(getX()+5, getY()); this will move the character 5 pixels to the right if the random number was equal to 0

I get this message java.lang.IllegalStateException: Actor not in world. An attempt was made to use the actor's location while it is not in the world. Either it has not yet been inserted, or it has been removed. at greenfoot.Actor.failIfNotInWorld(Actor.java:663) at greenfoot.Actor.getOneIntersectingObject(Actor.java:912) at Dom.<init>(Dom.java:55) at Cave_background.prepare(Cave_background.java:357) at Cave_background.<init>(Cave_background.java:21)

This is the enemy import greenfoot.*; // (World, Actor, GreenfootImage, Greenfoot and MouseInfo) /** * Write a description of class Drone here. * * @author (your name) * @version (a version number or a date) */ public class Drone extends Actor { /** * Act - do whatever the Drone wants to do. This method is called whenever * the 'Act' or 'Run' button gets pressed in the environment. */ public void act() { if(Greenfoot.getRandomNumber(5)==0) { setLocation(getX()+5, getY()); } } { Actor actor = getOneIntersectingObject(Drone.class); if(actor != null) { getWorld().removeObject(this); } } }

This is my player import greenfoot.*; // (World, Actor, GreenfootImage, Greenfoot and MouseInfo) /** * Write a description of class Dom here. * * @author (your name) * @version (a version number or a date) */ public class Dom extends Mover { private int speed=5; public Dom() { } public void act() { checkKeys(); } private void checkKeys(){ if(Greenfoot.isKeyDown("left")){ moveLeft(); } if(Greenfoot.isKeyDown("right")){ moveRight(); } if(Greenfoot.isKeyDown("up")){ moveUp(); } if(Greenfoot.isKeyDown("down")){ moveDown(); } } public void moveRight(){ setLocation(getX()+speed,getY()); } public void moveLeft(){ setLocation(getX()-speed,getY()); } public void moveUp(){ setLocation(getX(),getY() -speed); } public void moveDown(){ setLocation(getX(),getY() +speed); } { Actor actor = getOneIntersectingObject(Dom.class); if(actor != null) { getWorld().removeObject(this); } } }