Question

What is the item Monolith of planes and what is the use for it?

It is a reward from the Mysterious Ornate Chest Quest.

Comments

Ohhh good question. I see  some progress has been made since last time I looked.

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Opticorn Quest? Do you mean Mysterious Ornate Chest Quest with item like Opticording Sphere?

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Yes, the continuation of it with the black cube.

Answer 1

Item obtained from a Monolith of the Planes Kit. It is reward of Opticording Sphere Quest. 

You see a monolith of the planes kit.

It weighs 75.00 oz.

Use it in your house to construct a monolith of the planes... hopefully you know what you are doing.

Its light blinks in a frequency that can be translated to binary, with lights off as intervals and lights on as short or long bits. It takes 10 seconds for each state to start bliking with its code and there are three different states. 

The three blinking states display the following binary codes:

01000111 01000001 01001100 01010100 01001000 01000101 01001110 
01000001 01000101 01010010 01001001 01010100 01001000
01000010 01010011 01010100 01001000 00110100 01000101

These can be translated to text, resulting in:

GALTHEN
AERITH
BSTH4E

Galthen is a known character of the story, Scarlett Etzel's romantic pair. It's also in his grave that The Missing Piece of the Cube is found. The meaning of the other two words is currently unknown.

Source. Tibiawiki -Monolith of planes 

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