A simple Ontological argument

Today I will be considering a simple Ontological proof of God. Ontological arguments are basically attempts to prove God through concepts alone, without any real-world evidence. This particular variant has been fully discredited in modern times (and this is not just my atheist bias talking). This isn't so much an attempt to argue about God as it is an exercise in reasoning.

The Ontological proof is in three steps.

1. Definition: "God" is the greatest being imaginable.
2. Premise: It is greater to necessarily exist than to not necessarily exist.
3. Conclusion: God necessarily exists.

There is a very simple counterargument using what's called reductio ad absurdum. We show that if ontological argument works, various absurd results must also follow. Take the following example:

1. Definition: "Drod" is the greatest video game imaginable.
2. Premise: It is greater to necessarily exist than to not necessarily exist.
3. Conclusion: Drod necessarily exists.

Similarly, I could argue that the greatest sandwich exists, the greatest dad exists, and the greatest island exists. I do not even need to confine myself to objects of the form of "the greatest [blank] imaginable", nor do I have to assume any premises. Take the following:

1. Definition: The "IPU" is an invisible pink unicorn that necessarily exists.
2. Conclusion: the IPU necessarily exists.

I could continue to use this argument to prove the existence of anything, as long as I define it to necessarily exist. That is absurd. Unfortunately, while the reductio ad absurdum tells us that the ontological argument cannot possibly work, it does not tell us exactly where it goes wrong.

In my opinion, the central question of this argument is this: what sort of control do you have over objects when you define them? Normally, when I define something, I have full control over its properties. If I define a triangle to be a polygon with three sides, these properties must be true. There is no triangle with more than three sides, because if an object has more than three sides, it cannot be a triangle.

Why can't I do the same with the property "necessarily existing"? Let's try the same argument I tried with the triangle. "There is no God that doesn't necessarily exist, because if an object doesn't necessarily exist, it cannot be God." Aha! The argument with the triangle only proves that if there is a triangle, then it has three sides. Similarly, this argument only shows that if God exists, then God must necessarily exist. The Ontological Argument basically assumes what it is trying to prove. We fully control the properties of an object that we define, but we cannot control whether there is an instance of the object in the real world. (Some philosophers go on to say that existence cannot be a property of an object, but that distinction is irrelevant for now.)

In the spirit of critical-thinking fun, I shall attempt a similar argument going in the other direction. This isn't a serious argument, just what passes for humor in my mind. Any refutations?

1. Definition: "God" is the greatest being imaginable.
2. Premise: A being would be greater if its existence could be proven with the Ontological Argument.
3. Premise: The Ontological Argument is impossible.
4. Conclusion: God is impossible.