Hello,
When you playing game with second monitor, when cursor is not locked to screen, you can move cursor out of bounds of game window to for example. second monitor and click hotkey for skills when your cursor is on second monitor without game on.
Game is calculating distance between your cursor which is out of bounds and allows you to use skills on places which are not available to see on camera.
For example you can put wraiths at the end of monolith just after start or cast other skills which are cast at cursor location.
TLDR: Have second monitor, borderless window active, move cursor out of bounds to second monitor, use hotkey for skill - skill is cast in location of cursor on second monitor. Example Wraith with summon at cursor location node.