This is a guide on how to use the Compound System added on the Midnight Reborn Patch on August 18 2020.
What is it?[ | ]
The compound system is a way to use old accessories* that you DO NOT NEED anymore and combine them with runes from Midnight SkyPetal Plains (MSP) to get bonus stats.
*Legendary accessories only
The compound system can be accessed by the compound icon on the bottom right of your screen. 
How does it work?[ | ]
You click on the giant squares with plus icons (+) and PERMANENTLY put in an accessory. The level of the accessory directly determines the stats that you will receive later on. The accessories can be replaced with higher accessories to boost gained stats.
After putting in 2 accessories in adjacent boxes, you can click on the small circle in-between then to add a rune (etching stone).
These etching stones can be obtained by acquiring Lunar Twilight Flower from completing quests and killing enemies in MSP. I'm sure there will eventually be other ways to obtain them... such as event boxes.
You can exchange Lunar Twilight Flower for Etching Stones inside MSP at a vendor.
The quality (Green, Blue, Purple, Orange) will affect the maximum of stats possible. The stats applied are random and can be overridden by using a stone on the same location.
------------------------------------------------------------
| Hongmoon | Burnished | Searing | Exalted | |
|---|---|---|---|---|
| Sacred Crystal | 25 | |||
| Elysian Crystal | 5 | |||
| Soulstone Cystal | 25 | |||
| Moonstone Crystal | 5 | |||
| Sacred Orb | 80 | |||
| Elysian Orb | 20 | |||
| Soulstone | 80 | |||
| Moonstone | 20 | |||
| Gold | 40g |
Torrent: Mystic X, Boss Atk Power X
This is what the interface looks like when it is full.*
*This image is using the lowest possible gear and lowest possible etching stone.
FAQ:[ | ]
Q: Can you replace an item with an item of the same power potential?
A: No. If you place in a 190, you can only replace it with something higher
Q: Can you have 2 of the exact same accessories in the big squares?
A: No. The (6) accessories in the squares must all be of different names. Items of different specs can be used.