Wand of Symmetry

This magical gadget mirrors the blocks you place across one or more planes and places them automatically.
The Wand works passively while held in the hotbar.

• [Right-Click] on a block surface to create or move the mirror to that location.
• [Right-Click] while Sneaking to configure the mirror type and orientation.
• [Right-Click] in the air to remove the mirror again.

Once a mirror is visible at the spot you chose, block placement and removal will be multiplied by the wand, using Blocks from your inventory.

Configuration

Scroll on the input fields to select the mirror.

• Mirror Once Places a second block on the opposite side of the mirror, 2 Blocks will be used total.
• Rectangular Applies Mirror Once, and the perpendicular mirror again on both new blocks, creating 4 Blocks in total.
• Octagonal Applies Rectangular, and another diagonal mirror on the result, making it 8 Blocks after placement.

Best is to try out the mirror types and see the effect for oneself.