What happens to a shadow character when it is brought back into play from the dead or discard pile.

Ie. I use to be a dragon to bring back young griff from the dead pile.

Does he go to shadows or to the field?

"Targaryen only.Play only if you have at least 1 Power Struggle plot card in your used pile. Challenges: Stand a Targaryen character you control to put a character with a printed cost of 3 or lower into pla y from your dead pile."

It says specifically "Put into play", not "Put into Shadows".

The Shadows rules say that a card with the Shadows crest cannot be "Marshaled" directly into play. "Marshaled" means playing from your hand by paying its gold cost during your turn as the active player during the Marshaling phase. So this is the only circumstance in which Shadow cards must go into Shadows.

All other "put into play" card effects (like To Be a Dragon) can put a Shadows card directly into play without making to card go into Shadows first.

Don't forget the shadow cost - so if Young Griff is s1 his cost is 1 + 2 (for shadows cost)

You would not have been able to use that event card for a s2 character