The Ontological Argument - valid or debunked?

[Edwardo Piet]

My contribution:

Premise 1: It's possible that a 'maximally great being' exists.

Logically possible, yes.

Premise 2: If it's possible that a maximally great being exists, then a maximally great being exists in some possible world.

Premise 3: If a maximally great being exists in some possible world, then it exists in every possible world.

These are non-sequiturs.

Premise 4: If a maximally great being exists in every possible world, then it exists in the actual world.

Yes.

Premise 5: Therefore a maximally great being exists in the actual world.

No because "if God exists in all worlds then he exists in our world" proves nothing.

Premise 6: Therefore a maximally great being exists
Conclusion: Therefore God exists.

This is redundant.