A glitch that renders the limbs invisible. First, Make the spine segment you wish to put the limb on as small as possible. Tip: You might also want to make the adjacent segments minimum size, too. Then, take your limb and put it on the small segments. Make your limb as large as possible. Next, move the limb up a bit, so that they move, but don't connect. Then shrink the limb part touching the body as fast as possible. If done right, the limb(s) should be invisible. If not, try again, or find new instructions. If successful, you can use this technique to create fish that look like they're swimming close to the ground, or you can end up with a haunt that floats through the air. Have fun with it!
The easiest way to do this is to have one section at either end (preferably the front) brought down closest to the ground, then the limbs are added after that, same as before (enlarge it to the largest possible, pull up until it barely sticks on, then scale it down). Once that is done the rest of the body can be freely moved and, though you can't change the size of each body segment without needing to try all over again.
For fish-like movement, split the leg in two at the "knees", and space it at the widest possible, so it moves side-to-side (you might need to try this a few times to perfect the movement); for dolphin-like movement, drag the "knee" part high above body so it has to "jump" invisibly. The "hip" joint of the leg will also have to be in the front of the creature. However, adding limbs with hands will change the dolphin animation to a bouncing animation.
If you add exoskeleton limbs to the invisible ones using control, you can make multiple bodies in one!