Just flick the mouse right after you click to place multiple items.

[everennui]

In GZDB.

I figured this one out by accident.

What are some other good shortcuts?

[scifista42]

Why some if you can get them all? Look into "Help -> Keyboard Shortcut Reference".

[everennui]

scifista42 said:

Why some if you can get them all? Look into "Help -> Keyboard Shortcut Reference".

It's not in there.

[scifista42]

What, "Keyboard Shortcut Reference" is not in "Help"? Then update your GZDoom Builder. And well, it's actually called "Keyboard Shortcuts Reference". Or do you mean that your newly discovered shortcut is not listed among the shortcuts in the reference? That may be because it's not so much a keyboard shortcut as it's an exploit of the Classic Mode shortcut named "Edit", which (as described in the reference) can either create items, drag them, or open their properties, depending on context.

[MaxED]

PROTIP: You can duplicate selected things by shift-dragging them.
PROTIP №2: There is a Help side panel which shows context-sensitive list of most/all actions used by current editing mode.

[scifista42]

The Help side panel is a great one, thanks for making me know about it! (in my previous posts, I was talking about the Help tab on the top panel)