Grounder is a second-generation Badnik created by Dr. Eggman. Appearing in Sonic the Hedgehog 2's Aquatic Ruin Zone, the Grounder is a remodelled version of the Burrobot. It has a larger body and is actually faster than its predecessor. It does not burrow underground, however. Instead, it hides behind cover and burrows through walls to catch Sonic by surprise.
Sonic the Hedgehog Yearbook 1992
In the UK-published Sonic Yearbook, Dr. Robotnik built a series of giant-sized Badniks, including Grounder, to destroy Sonic and Tails. Sonic and Tails attacked the giant Grounder only to bounce off its reinforced body. Refusing to give up, Sonic tried attacking from above, getting atop a large stone column and launching a Spin Attack on the Grounder's head This attack worked and the giant Grounder was destroyed, releasing the three animals trapped inside.
Sonic the Comic
Grounders made only a single appearance in STC, during the "Robotnik's Revenge" two-art story. In this story, Dr. Robotnik had discovered the Freedom Fighters' secret base in the Emerald Hill Zone and personally led an army of Badniks -including Grounders, Crawltons and Tunnelbots- to destroy it.