This is a Spider Walker, it is the last droid walker the CIS built. It is also known as the Spy Droid.
About this creation
One day, Count Dooku contacted Greivious and told him that he wanted a droid that could go on spy missions with his apprentice Asajj Ventress with out being seen. He wanted a droid that could do things that other droids couldn't do without tripping, or falling, or being killed very easily. Count told Greivious that this was top secret! Know one could know about it, not even the Separatist Council! So Greivious went to work with out telling anyone of course, he gathered up scrap metal and started building it. He used all four of his arms to make the work go faster. But one odd thing especially Greivious, was that he did not add guns! He did not add any weapons! He did program it to fight until his opponent was dead or it lost a leg, then thanks to the tracking devices that were on it they could come and rescue it before any major damage was made. The droid was very powerful, it could jump very high! Greivious took this as serious as the plans for "The Ultimate Weapon" if the Republic found the plans for that, the Separatists would be in for a big surprise!
Top view of the Spider Walker.
The droid's front feet were tracking devices, but they weren't on all the time! You had to turn them on!
The Spider walker was programed with many modes, her it is in walking mode.
The droid in expansion mode, this was for when the droid is is deep sand or snow.
This is the droid in rolling mode.
When the droid was finished Greivious oversaw it and made sure it was ready for war. For this droid would later be on many planets.