All the mobs are jumping too slowly or fast and some mobs, like slimes, don`t have the special animation anymore, when they hit the ground while moving

This ticket is very difficult to comprehend, please use the Bug Report Guidelines here when posting issues.

Load a world and observe the behavior of passive mobs, esp. chickens in water. They lag forward (do not move smoothly) and are very slow.

I don't experience that in the current snapshot (14w25b). The complete output of the development console and a manually triggered crash report (hold F3 + C for 10 seconds while in-game) may help diagnose the issue.