Centered Path is the second upgrade of Path 3 for the Monkey Ace in BTD6. It adds a new targeting option "Centered Path" that sends the Monkey Ace along a circular path along the center of the map. It doesn't matter where the Monkey Ace landing pad is for a Monkey Ace set to Centered Path; they will all loop around the same path, albeit different parts of the loop depending on timing at which the player changes the loop setting.
It costs $255 on Easy, $300 on Medium, $325 on Hard, and $360 on Impoppable.
This upgrade is one of many upgrades spelled in American English. What makes this fact interesting is that Ninja Kiwi is a New Zealand company, despite primarily using British English, especially when "-re" words are normally spelled as "-re" in New Zealand instead of the American "-er" (e.g. "meter" for "metre", or in this case, "center" for "centre").