A rather unique fight, the Guardian (ガーディアン), found at the end of Sandopolis Zone Act 1, is a stone statue that doesn't even look like a robot, and has no weapons, but jumps toward you. You can knock it back into its shell form by jumping and hitting its head but cannot hurt it this way. To defeat it you must lure him to the left and get it to jump in the quicksand pit. That's the only way to defeat it. The most efficient method of doing so is to stand on the edge of the pit until it gets close, then jump into the pit and jump continuously to avoid sinking. Make sure you're far enough away so that it doesn't jump on you (although it can't crush you if it does jump on you; it merely damages you). It will jump into the quicksand and blow up.
It is also possible to beat this mid-boss by standing on the right side of it and hitting him on the head repeatedly. Though this avoids the possibility of it jumping on Sonic when it reaches the pit, it also takes longer for it to do so.
This opponent can prove unexpectedly difficult to defeat with Super Tails, as his Super Flickies are just as likely to knock the Guardian away from the quicksand as towards the pit.
When playing in Sonic & Tails collab. mode, Tails can either help or hinder you. If you choose the first method of standing in the pit to lure it to you, Tails could knock it back by mistake, towards the right. If you decide to knock the Guardian all the way back, you can get Tails to stand in front of you such that when you jump and touch left, he does the same and (hopefully) hits the Guardian on the head. This latter method is a good idea if you have a lot of rings (that you wish to keep) but no shield.