But this in the class that you want to have the life--;

@JetLennit, that will create a new player instance and decrease its 'life' value. I am sure that DownKost wants to change the life value of the player object that is already in the world (not a different one). You need to get a reference to your player object (the one that you wish to decrement the life of). If you only have one player, then '((Player)getWorld().getObjects(Player.class).get(0)).life--' . If 'life' is a private field, you will need to have 'get'/'set' or 'add' method(s) for the field and use them to change its value instead of changing the value directly but you would still get the reference to the object the same way (if you do not already have a reference to that player object.