This Seeking Tech guide will show you how to find the third and final puzzle piece from the Spooky Time stage in Astro Bot.
This collectible is located all the way at the end of the level.
Once you get there, use your power-up to stop time so that you can jump to the two columns in the middle.
You then need to stop time again in order to line up the puzzle with the glass ball at the end of the stage. Once you got the right alignment, grab the collectible and then complete the level.