1: Twist bones would normally influence the upper portion of the thigh and forearms. This is a quick sample video:https://www.youtube.com/watch?v=0H5DIDZcGVU
It makes things look better. It may just not be influencing anything in the sample mesh you’re working with but a real character would have upper thigh, upper arm, lower forearm, and lower shins rigged to the corresponding twist bones. That’s how I’ve done it at least.
2: I’m not entirely sure what the IK thing does since it’s not really documented but I ended up finding a use for them myself. I think I only remember seeing these in the UT3 models that came with UDK and haven’t seen them recently in UE4. I actually took them out in my UE4 game since I found better ways to do this with the anim event graph.
I was setting the positions of the IK control bones to some world position using some skeletal control that sets their absolute transform. Then the hands would try to IK to the transform of those bones if that makes sense. In UE4 I just get the transform directly from code in the anim graph and find basically no use for these IK bones.
If anyone else has a better explanation I’d be interested in hearing it.
3: Toe is called ball because it’s the ball of the foot. Heh, yeah… I think it’s actually not the toe but the part right before the toe which is the ball of the foot.
4: IK Gun Bone might be an offset from the hand where to actually place the gun relative to the hand. I think this is what you’re talking about?
5: Not sure I completely understand the question. I think they need to be in whatever placement you want them to be relative to the ground. When the foot IK kicks in it should move the feet to the right height so they stand properly on stairs. And then I think you want to rotate them to align with the slope. Whatever pose they are in will be preserved but rotated and repositioned relative to the ground if you set it up right.
I’ve seen in assassins creed for example, the character starts posing the foot a little differently to make it look more like its standing on tip toes. That probably takes extra code if it happens automatically somehow.