The use of 'static' is not something that is limited entirely to greenfoot-- it is a part of the java language itself (see Class members in the java tutorials). The message is saying that you are trying to call a method without supplying any object (of the class the method is in) to execute the method on. You are supplying a class name, which does not point to any particular object, but to the class itself. All 'public static' members of a class can be accessed by using dot notation of the name of a class followed by the member name. However, the method or field (member) you are trying to access is not 'static' -- it needs an object of the class to execute on or for. In other words, the class is not what is taking damage, but some object that is created from the class, which you will need an object reference to. For detailed help on this, you will need to supply the code you are trying to use with a brief explanation of what it is supposed to be doing. Supply class names for where the code given is in and where the method being called (takeDamage) is in.

Thank you for explaining how that all works! I just figured out the problem, I just needed to add 'import java.util.List;' Completely forgot about it haha. Everything is working as intended!