A Tale of Two Todds SPOILER ALERT
I'm not referring to the jarring changes in appearance of Todd, but to the differences in the portrayal of the character.
In the series, he just struck me as a polite, well mannered guy with no conscience who did whatever was necessary to keep from getting caught. He never had that creepy horror movie vibe he displayed in El Camino. The El Camino Todd seemed more like a genuine serial killer. Basically, two entirely different Todds. I guess you could explain it by saying Todd was showing his real self to Jesse in El Camino when they were alone together, and in BB he was always keeping up a more 'normal' front for Lydia, Walt, Uncle Jack etc.