Board Thread:Manga/@comment-31982730-20170606191843/@comment-4929778-20170623151236

In season 2 or the COTT arc we find out Titan shifters have the ability to turn off the regeneration if they so desire as Reiner did it so nobody would suspect him after a Titan broke his arm. And in season 1 we find that some Titan shifters can focus their energy into one organ to grow it back quicker which is why the female Titan regrew an eye after less than 30 seconds when normally it takes a couple of minutes. Since four years have passed it'd be pretty reasonable to assume eren is better in tune with his powers that he knows more talents.

And as for eren having the armband on the wrong arm and being a bad spy remember he never grew up among the Marley so he probably wouldn't know, and eren is pretty impulsive. Plus the soldiers were being sent to the hospital so eren cutting off his leg would allow him to look more like a crazy soldier in need.