Rain of TNT is the cloud that will defend the mobs, players or anything.
Step 1: Start With Flat Area and Make a Line
Get TNT and Lava from inventory and make the vertical line of TNT to make sure.
Step 2: Horizontal Line Then Vertical Line Removal
Make a horizontal line of TNT and make the removal of vertical line to make sure that is the behaviour is good to look like the cloud.
Step 3: Working
Your rain should be the TNT, and cover the horizontal line of TNT with the lava, then the TNT working in several seconds because of lava and fire, and should be the working TNT with the TNT falling down.