Godmodding is the process of making your own characters or creations more important, more powerful or more central at the expense of those created by other authors.
Don't destroy other works
Deliberately making the creations of other authors appear weak, incompetent or plain worse to make your own look better by comparison is wrong and unethical.
Don't overpower your own works
Likewise, making your own characters reach godly heights of importance and power is also to be avoided. Like the infamous Mary Sue, overpowered characters remove narrative tension, and therefore reader attention, by making it impossible for the main character to fail. This is not to say that very powerful characters should never be written. However, you should be careful to ensure that a sense of real stakes of some kind is preserved.
What to do instead
Respect other people's works. Make sure you consult authors before using what they've created. They might even find your perspective on their character helpful in their own writing. In return, they can offer novel points of view on your characters. Critiquing and collaborating with people helps build more rounded characters and plots less prone to holes and the pitfalls of narrow perspectives. This, in turn, will make resulting works better and more enjoyable to read.
Don't try to destroy other people's works, but instead build each other up.