Oh, Garth. How I love him. But it’s so hard to predict his actions because it will all depend on how events play out.
After all, this is the guy who killed the tooth fairy.
So, if the smol brothers are up to shenanigans, they should be sure to duck into hiding if he’s around. If they’re in trouble, there’s a good chance he’ll help out these very strange curse victims. If it’s just Sam smol, Garth will have a Dean solidly in between him and Sam until Sam gets his overprotective big brother to chill.