Hi! A question just to be sure i understnad it...

Sneak Attack + Gandalf (core) can be played during Quest phase in the Commit characters action window? I mean...could we play events in that window? So that i will be able to commit Gandalf to the quest? I assume that after Staging if we play Sneak Attack + Gandalf (core)..we cannot commit Gandalf to the quest..right?

When exactly can we play Sneak Attack + Gandalf (core)...to be able he is commited to quest ?

Yes, just Play the combo in the action window before committing characters to the quest.

http://www.lotr-lcg-quest-companion.gamersdungeon.net/#RoundSequence

Are you talking about the Quest phase Step 1 - Commit characters window?

If you play Sneak Attack - Gandalf before you commit characters, yes, I can commit to the quest as well.

If you do it after staging, then no he cannot commit to the quest.

Take a look at the post above