Arm crunches when bent

[ATTACH=CONFIG]493886[/ATTACH] I’m having this 2-D animation problem where when I move the lower half of the arm, the upper half is weirdly crunching. How can I fix this?

Not a technical issue, but you should look into changing the weight painting.

I tried fixing the weight paint and now it’s like this[ATTACH=CONFIG]494249[/ATTACH]

This “shrinkage” is a general problem of many bone animation algorithms, weight painting can not fix it. You can try the “Corrective Smooth” modifier.

Also, you need more geometry, otherwise your texture coordinates will distort heavily. Add in a subdivision modifier (simple subdivision is fine) before the armature modifier.