A fluorescent lime green
Ñ or a teal blue
Ñ? The first is a night troll/creature (which will be described with other sinister names), the second is a zombie.
This sounds like you are talking about night trolls
Ñ who happen to be very strong, incredibly fast, and feel no pain. When they are armed with a weapon they feature no grab attack since they default to strike. But when unarmed (which you will notice when you inspect them) the grab attack is mixed in with the strikes which makes them much more dangerous.
The safest combat tactic is multi-attacking quick attack (targeting legs and arms first) + dodge away as Nikow mentioned (after you've led
Ñ out of their lair), but only when you notice they are not about to grab you, as multi-attacks will slightly nerf the benefit of quick attack and dodge away, and you'll want your best chances of dodging which means dodging away manually as a single action. Never dodge adjacent since grabs (when they surreptitiously occur) can be broken only when you are moving away from your opponent. Dodge adjacent can also cause you to be on the receiving end of additional strikes.
Worst case, if you are grabbed and you're standing side by side not quite friends, you'll grip break by slashing the limb that's doing the grabbing. Depending on the situation (how fast is he/she/you, and how strong are you), you'll choose to quick attack or just normal attack your slash. The goal is to sever the limb. Your chances of doing this have to do with how high your weapon and fighter skills are, particularly when the choice of attack is shown as being tricky or difficult. If you fail to sever and the next move is joint lock, you're dead. There is also luck. Sometimes the next move after the grab will be releasing the grab, or your opponent will try to strike you, instead of the joint lock. You'll be able to swing at the grasping limb again, hopefully with better result.
Also here is an old but info filled thread about zombie combat:
http://www.bay12forums.com/smf/index.php?topic=143991.30