I'm not certain how we get the 2nd ending, but you jumpscared me good!
Thanks for the video O Captain! Second ending requires to obtain bunny arms from the gagged up bunny in the ally (red ally, near the gun shop). Shoot the arms off (or use axe which you can get near the cat), then return to "devil bunny". Honestly it's quite short and done to cause some rage moments, so not exactly worth the effort.