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Secret passage is best used to try and get more secrets after you've played Hanar. Get it, secret..passage ... yeah.
As far as what to mulligan I generally will never keep a scheme. Yes I understand it builds while in your hand over time. It's a late game card and best used on, well obviously blackpaw is ideal, which card go best use it on would be a game to game basis.
Playing a 5+ scheme on a deathrattle followed by a roll the bones. You can easily refill your hand.
If playing aggro decks you could use a scheme on Elven Minstrel to keep a flow of minions till they lose steam.
Lab Recruiter is ideally for Jade Spirit to help with tempo. Jade swamer is merely a fill card to add a stack to the jade counter, it also helps while deck digging using roll the bones. If you play this deck around jade swarmer you'll probably lose alot. Id say this is more a midrange deck.
This deck has alot of rng based effects so its difficult to give a guide. I can provide what combos and synergies have worked best for me, but they are also situational.
Best tip. Don't use your secrets until you need to. Hanar can work wonders when played right.
I hope this helped some. If any specific questions on synergies leave a comment.