EDIT: This was one of my first trophy guides, so I didn't realize that the video on its own wasn't helpful. I've attached a brief description found of playstationtrophies.org (as I cannot remember exactly how I got it because its been so long)
Go to Create Mode via your Moon. Make sure Advanced Create Mode is on by pressing
, then go down to Settings, then go down to PROFILE.
Make sure Advanced Create Mode has a check next to it, then exit the menu.
Make sure the game is paused by pressing
. It will be paused by default if you entered a new empty crater on the Moon. Pause will make sure everything stays in place while we set this up. Open your Popit and go to Global Stuff.
to go to the Gameplay Controls category then go down to the Water sub-category. Raise the water level by pressing
, it does not need to be a whole lot.
Now return to the Popit menu and go to the Tools Bag. Press
to go to the Creatures and Characters category. Go down to the Sackbots sub-category and place a Sackbot above the water. Now back out and using your Popit Cursor, press
over the Sackbot to tweak its settings.
Go down to the A.I Tweaks, there will be a setting at the top right with an image of water that says Can Swim: Yes or No depending on the setting. It is set to No by default so change it to Yes.
Now back all the way out of your Popit and unpause the game by pressing
on the D-Pad so the Sackbot falls in the water, and the trophy should unlock.