Hi Jade, thanks for the video. Glad to hear you enjoyed the game but in the end it was good thing that you could not help the bunny, unless you enjoy rage moments.
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.