Critique you want, ey?

Although fairly short, you've managed to handle the simplicity of this emote extremely well. The shading is perfect, the animation of the string looks fine to me, and the expressions are really great as well. The 'holy crap wtf' look on the balloon fits it so well. But, although it's fantastic, I think they're are some minor things you can do to improve this to make it perfect!

For starters, the stationary hand of the green, the one holding the balloon, could be bobbing up and down to show the physics of the balloon slightly more clearly. Of course, not that it's a problem now. I am clear of the fact that if you do decide to follow through with that suggestion, the whole animation of the ballon, the bobbing of the balloon's hands and especially the string will have to be changed. That's something I'm too lazy to create, if you ask me. But go ahead if you want to.

I think you could also add some frames for the greenie to blink. His blank never-ending expression doesn't really suit the grin and the idea. However, I understand if the green's expression is supposed to be looking creepy. I just don't think, personally, that the two-pixel eyes suit the creepy look. Maybe tard eyes, or large white eyes with small diluted pupils could fit? Just a suggestion.

Overall though, you've done a great job on such a simple but excellent idea. It's looking fine now. Unless you want to improve this, keep it as it. I'm just fussy sometimes.