Extraordinarily flexible creatures like snakes and octopi are not all that much harder to keep hold of than less flexible critters (or people), even very large ones. When these critters fight each other, they are not able to escape from each other's grip whenever they want to. This suggests the bonus for escaping from a grapple is too large. On the other hand, their flexible bodies are quite capable of holding their prey and rivals, suggesting a bonus for fighting in close quarters is warrented. I make the following changes:
Flexibility only gives a +1 to break free in close combat, but it also gives +1 on just about everything else in close combat; including: holding an opponent in a grapple, pinning, resisting a pin, and performing a choke, strangle, constrict, or choke hold. You get the whole +3 bonus when resisting any joint lock, limb wrench, or neck snap. It does not help you hit, initiate a grapple, or perform a takedown or joint lock.
Double Jointed increases this close combat bonus to +3, or +5 when resisting a joint lock, limb wrench, or neck snap..
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