I really liked the turnip monsters (white punkins?)that appeared near jack. I took a sequence of screen shots and made an animated gif out of that. You can get into legal trouble posting gifs from movies and sometimes games, some art sites remove them and punish users if they can't prove they had permission to use the images when posted. This is only fun, not for profit, may I have permission to post my ” dancing turnips” gif please?
As long as you aren't trying to defame/profit you shouldn't worry too much about that. Noone will go out of their way to smack you just because you made a gif for fun.