According to Vince Gilligan, Felina is the Crystal Blue. He was most comfortable with the chemistry and the lab was his favorite place.

In the last one he talked about a dark idea that didn't come to fruition as they didn't kill Jesse as originally planned. Walt was going to kidnap the bad guy that killed Jesse and very painfully dismember him a little every day but setting up a rifle with a trip wire that points directly to the bad guy's heart giving him the option to end the torture by pulling on the line.

The bad guy won't pull the wire regardless of the torture and eventually Walt Jr stumbles upon the scene and has no clue why this guy is tied up and tries to offer him help. The bad guy figures out it is Walt's kid and pulls the kid in front of him and pulls the wire killing them both.