We can make a more complex transition for a bit of extra game juice.
Locate the Transition image in the Pixel Adventure assets OTHER folder:
Create a New Scene with a Node2D as the root
Rename it to Transition Tile
Use the Transition.png as the Texture
Add an AnimationPlayer as a child
Set the grid size to 44 x 44 and turn grid snapping on
Duplicate the Sprite2D node and place it on the next snap away from the current Sprite2D
Continue duplicating and moving sprites until you have completed a row at the top of the screen
Adjust the grid stepping to 22px by 22px
Because we are now going to duplicate the entire row and file the gaps
Select all the nodes which make up the top row, duplicate them and move them down and to the right
Duplicate again and move them down and to the left to fill the gap
Repeat this process until you have covered the entire viewport
Now select the AnimationPlayer Node and click on Animation then New and name the animation Shrink
Select ALL of the duplicated sprite nodes
Find the Transform -Scale Property
 Click on the Key next to it
All of the scale tracks for all of the Sprite2D nodes will be added to the Animation
Change the duration on the timeline to 2 seconds
Move the timeline to the 2 second marker
Se the scale to 0.0 and hit the key again
Select the autoplay on load so that the animation plays as soon as the scene loads
Play the animation and you will see the diamonds shrink away.
