Crack theory time!
Rumple and his brother Peter were very close as children. However, they had a father who treated them poorly and the two boys decide they need to get away from him. Rumple receives help (I want to say Blue but she isnt in the credits. boo) and is given a way for him an his brother to escape their father:Pandora’s box. However, Peter, being curious about the boxes powers, opens it prematurely. All of the bad entities that reside in Pandoras box rushed out and into the nearest living thing – Pan. Because of this, Pan becomes the big baddie we know (and love) today.
HENCE why Rumple fears him – he knows what he is made of.
Something like this happening would be awesome!