Let's say Nick is the one who's talking. So Nick is the one talking with no animation shown. How can I do that?

See that option called "Animation control"? Set it to "Do not speak". It's that simple.

Do you mean making Nick invisible?
If that is so, put in custom animations an invisible .gif, and then use that one in the message.
If there is a character, simply select the character appearing on the screen, set it to "Do not speak", and set the display name to "Phoenix".

If you mean like if he was thinking, do as henke said

There is no need for a dummy transparent image, just don't pick any pose.

Nop, because if you put "previous image" (Or whatever), it takes the last sprite used for that character (It does to me)

Nope. All you have to do is use "previous picture". If you want to have no character sprites visible when you do that, you should use "hide character" and then use "previous picture".

Thanks, Meph