Originally Posted by
Cernunnos
Half if not all the ones they mentioned as not being summonable outside of Winter veil require snowballs to summon.
If it were not for the engineering thingy that makes snow balls these pets would not be summonable outside of winter veil anyways, due to requiring a snow ball to summon them in the first place.
No other pets that come to mind immediately have such a requirement.
The wolpertinger does not require hops
the spring rabbit does not require an egg
Tiny snowman requires a snow ball to summon.
Winter's helper (the gnome) requires a snow ball to summon