[Soyweiser]

Jon, those items disappear. Unless there is a lab, then they might get placed into the storage.

There is no hidden retainer.

You can get your own hidden retainer by using scouts.

Regarding skrattir this is what I remember:
Changing before battle. No changes of shape during battle.
Changing during battle, the shape moves one shape after battle wolf -> giant, werewolf -> wolf, etc.

I think, not sure, that a giant skrattir that is killed transforms into a werewolf, and becomes a wolf after battle. Not 100% sure on this one. but this should be easy to test.