Each Unit in this game series means each 1 of the character in the scene:
Edge scrolling viewport by mouse
Create BP pawn, called CameraPawn
Add spring arm (target arm length: 0, Enable Camera lag in details)
Add camera, rotate Y -70
Drag the pawn in sky of scene, Auto possess player set as Player 0
Go back to Camera Pawn, event graph:
Add Mouse X (move left-right), add float variable Scroll Speed, set vaule as 600 cm/s
For left movement: (when mouse position divide by viewport size larger than 98%, or smaller than 2%, it moves)
For right movement, extend as:
Duplicate the nodes above to Mouse Y node
Change location X to Y on relevant nodes, and delta location becomes X axis
Lock the mouse in viewport, not let it go out
Open BP TopDown Controller, event graph, add follow