If i'm playing solo and this northern warg comes as a shadow card, should i decleare a new character to defend this new attack or can i defend with same defender i used in first attack?

If you're playing solo, that shadow effect does nothing, as there is no 'next player' to engage.

Thank you

When that warg-fetching treachery came up, I always took this Warg out of the deck... hate that shadow effect!