Possible cause is an outdated Java version
At least MC-68102 got fixed by installing current Java 1.7.0_67 from http://www.java.com/en/download/ or 1.8.0_20 from http://www.oracle.com/technetwork/java/javase/downloads/jre8-downloads-2133155.html
Most mobs look either oversized or broken
Related issues
is duplicated by
MC-64093
When I spawned some mobs in superflat they had stretched textures. The preset was overworld with no grass, lava lakes, or lakes.
MC-67625
Giant glitching Slime
MC-68102
Giant weird sheep
MC-68483
Skin Not Rendering properly
MC-69143
!!!PIGS WITH NO FEET!!!
MC-69549
Huge rendering glitch on mobs
MC-69587
Skin model completely messed up
MC-69722
rabbit render
MC-70175
Minecraft Player Model is looking weird......
MC-70435
Model Glitch On Minecraft Realms
MC-70563
Invisability and Glitches
MC-70641
The Minecraft reference skin "Steve" has a render issue
MC-70952
Enderman missing limbs
MC-70998
cave spider
MC-71013
I dont know what to call this but it need to be fixed
MC-71364
Mobs resize and when they shrink they seem look like failed models,etc...
MC-71969
Player Models Are messed up
MC-72071
VERY buggy mob models! What the heck?!
MC-72299
Big Mobs
MC-72355
Bat models are glitched
MC-72627
Error Rendering Mobs
MC-72775
Upside Down Nameplates, Shadows, and clipping upside-down mobs.
MC-73334
SEVERE - Mob Models and Textures glitch and become invisible
MC-73363
copied chunks and glitched mob models
MC-73722
Minecraft Mobs have messed up textures
MC-73838
Rendering Bugs in 1.8.1-pre3
MC-74417
Mobs look very wierd
MC-74673
Mobs do not appear, Game glitches badly after rendering 8+ chunks
MC-78072
Wrong chicken texture!
MC-90149
Mob Glitch
MC-90254
Entity Models Glitching
Attachments
Comments
migrated
kumasasa
Please force a crash by pressing F3 + C for 10 seconds while in-game and attach the crash report ([minecraft/crash-reports/crash-<DATE>-client.txt|http://hopper.minecraft.net/help/finding-minecraft-data-folder]) here.
kumasasa
Please update your Java to the latest version (1.7.0_67 / 1.8.0_20): http://www.java.com/en/download/ and report if that has resolved the issue.
When using a 32-bit browser on a 64-bit operating system the automatic version detection will only show the 32-bit version of Java, the 64-bit version needs to be downloaded manually: http://www.java.com/en/download/manual.jsp.
migrated
I found the problem here. Some of the duplicates do have the right Java version. But what else do they have in common? An AMD/ATI. Seems like AMD has another huge bug, together with MC-62958.
Sonicwave
I'm not sure if this belongs here, but I think I managed to reproduce a variant of this in 1.8.1-pre2. (Attached screenshot.)
Nvm that was with a resource pack, I'll see if I can reproduce it in Vanilla.
migrated
I have reproduced it in 1.8.1 pre 2. MC-73334 screenshots are there. No resource packs, latest java version. AMD graphics card. Hmmm....
Sonicwave
Can confirm for 1.8.1-pre2 as well.
Sonicwave
Confirmed in 1.8.1-pre3.
marcono1234
Can confirm what StevenNL2000 said, it happened for me in earlier versions also in combination with MC-62958