How to configure Errtel and Mysterious Stone in MU Online

If the Pentagram is the chassis of MU Online's elemental system, the Errtel are the engine — and the Mysterious Stone is the workshop where that engine is tuned. Configuring this trio well is what separates a server with a "decorative" elemental system from a server with an addictive endgame progression, where the player spends weeks hunting materials and risking refinements to turn a common Errtel into a devastating piece. It is endgame content par excellence: it provides a long-term goal, heats up the economy, and creates stories of "I broke three Errtel before the fourth hit +9".

The tricky point is that Errtel, Mysterious Stone, and refinement form a system with many levers: rank, options per rank, refinement chance, protection against failure, material consumed, and balance against elemental PvP. Pulling one lever without thinking about the others creates a server where either no one can progress (frustration) or everyone has everything in two days (boredom). This guide walks through the complete configuration of these items, treating file names and values as examples — they "vary by emulator" — while keeping the concepts real and reusable. If you don't yet have the Pentagram and Elemental System up, start with the server base in the guide on how to build a MU Online server and set up the elemental system before refining Errtel.

Prerequisites

• Pentagram and Elemental System already working. Errtel and refinement are the layer above the Pentagram; without the elemental base, there is nowhere to slot the pieces.
• Client synced to the correct season. Errtel, Mysterious Stone, and the refinement interface need to exist in the client.
• Isolated test environment. Refinement affects PvP power; test everything outside production.
• Backup of the GameServer configs, the ItemList (server and client), and the database.
• GM accounts with items to spare to simulate dozens of refinements and measure rates.
• Progression spreadsheet. Record how many materials and attempts each rank requires, to calibrate the curve.

Understanding Errtel, rank, and options

The Errtel carries two kinds of value: the element (fire, water, wind, earth, or darkness) and the options (attribute lines such as elemental attack, elemental defense, and specific bonuses). When slotted into the Pentagram, these options add to the character.

The rank is the Errtel's quality level. It determines:

• How many options the Errtel can carry (more attribute lines at high ranks).
• The power of each option (larger values).
• On many emulators, which special options are available.

Think of the rank as quality stars: a low-rank Errtel has few weak lines; a high rank has several strong lines. That is why the endgame revolves around raising the rank of the Errtel — and that is where the Mysterious Stone comes in.

The table below is a conceptual example of progression by rank (values vary by emulator):

What the Mysterious Stone and refinement are

The Mysterious Stone is the central material in the Errtel's refinement (upgrade) process. In refinement, you combine the Errtel with Mysterious Stone (and, depending on the emulator, other materials) to try to raise the rank or improve the options of the Errtel.

The crucial point: refinement is probabilistic. Each attempt has a success chance. On failure, depending on the configuration, the following may happen:

• The rank simply does not rise (soft failure).
• The material is consumed with no result.
• In harsher configurations, the Errtel may lose rank or even break.

It is this risk/reward tension that gives the endgame its excitement — and it is exactly why it must be balanced carefully.

Step 1 — Register Errtel and Mysterious Stone in the ItemList

Before any refinement, the items need to exist on both sides.

1. Confirm that the Errtel (of each element) and the Mysterious Stone are in the server's ItemList, with their own section and index for the season.
2. Mirror the same entries in the client's ItemList, at identical indices.
3. Check names, icons, and inventory size.
4. Test with a GM: generate an Errtel and a Mysterious Stone and confirm they appear correct.

Like any item, if the client does not have the entry at the same index, the result is an invisible item or a disconnect when handling it.

Step 2 — Configure the options by rank

Now define what each rank offers. This is the heart of power balancing.

Conceptual configuration example (illustrative format, varies by emulator):

[Errtel]
; options unlocked by rank
Rank0_MaxOptions = 1
Rank1_MaxOptions = 2
Rank2_MaxOptions = 3
Rank3_MaxOptions = 4

; value ranges per option (min-max)
Option_ElementalAttack = 10-80
Option_ElementalDefense = 10-70
Option_SpecialBonus     = 1-5

; which options each element can receive
Element_Fire_Options  = ElementalAttack, SpecialBonus
Element_Water_Options = ElementalDefense, SpecialBonus

Guidelines:

• Grow the power gradually. The difference between ranks should be felt, but should not make the previous rank useless.
• Align with the Elemental System's ceiling. If the elemental system has an attribute cap, make sure a max-rank Errtel doesn't blow past that cap on its own.
• Differentiate elements by option. Giving slightly distinct options per element reinforces build identities without breaking the advantage cycle.

Step 3 — Configure the refinement rates

Here you define the endgame's difficulty curve. It is the most powerful lever and the easiest to get wrong.

Conceptual example (varies by emulator):

[ErrtelRefine]
Enable = 1
; success chance per target rank (%)
Rank1_SuccessRate = 80
Rank2_SuccessRate = 60
Rank3_SuccessRate = 40
Rank4_SuccessRate = 20

; Mysterious Stone consumed per attempt
StonePerAttempt = 1

; behavior on failure
OnFail = KeepRank      ; KeepRank | DropRank | Break
; protection item reduces the failure penalty
ProtectionItemEnable = 1

Calibration recommendations:

• High success at low ranks, low at high ranks. This gives fast progress early and real challenge at the top.
• Choose the failure behavior carefully. KeepRank is friendly; DropRank/Break increase risk and demand for materials, but frustrate more.
• Offer optional protection. An item that prevents rank loss on failure gives the player control over the risk and makes a great shop/event item.
• Think about the economy. The harder the refinement, the more Mysterious Stone is consumed — which only works if the Stone source keeps up with demand.

Step 4 — Configure Mysterious Stone sources

A challenging refinement is pointless if there is no material to attempt it.

1. Define where the Mysterious Stone drops: high-level spots, events, bosses, quest rewards, or the shop.
2. Calibrate the drop rate according to the refinement's difficulty. Hard refinement requires a larger flow of Stone.
3. Avoid single-source bottlenecks — if only one boss drops Stone, it becomes a toxic point of contention.
4. Consider an additional sink (trading items for Stone) to give players an alternative route.

Step 5 — Assemble the refined Errtel on the Pentagram

With the Errtel at the desired rank, the player puts it to use.

1. Opens the Pentagram assembly interface.
2. Slots the refined Errtel into the slot matching the element.
3. Confirms the assembly — the Errtel's options (now stronger from the rank) add to the character.
4. Equips the Pentagram.
5. Checks in the status/combat screen that elemental attack and defense rose according to the rank.

The gain of a high-rank Errtel over a base one should be visible in PvP — that is what rewards the refinement effort.

Step 6 — Test the complete cycle

Test the entire process, not just isolated parts.

1. Generate a base Errtel and Mysterious Stone with a GM.
2. Refine several times and measure the real success rate — it should match the configured one.
3. Force failures to confirm the behavior (KeepRank/DropRank/Break) and the protection item.
4. Assemble the refined Errtel on the Pentagram and check the attribute gain.
5. Duel to validate that the high rank truly weighs in elemental PvP.
6. Based on the tests, estimate how many Stone an average player spends to reach the max rank, and adjust rates/sources.

Common errors and fixes

Launch checklist

• Backup of the GS configs, the ItemList (server and client), and the database
• Errtel (all elements) and Mysterious Stone registered at the same indices on server and client
• Options per rank configured with gradual progression and within the elemental cap
• Refinement rates defined (high success early, low at the top)
• Failure behavior chosen and protection item configured
• Mysterious Stone sources calibrated for the refinement's difficulty
• GameServer restarted in the test environment
• Real refinement rate measured and matching the configured one
• Rank gain validated on the Pentagram and in elemental PvP
• Average Stone cost per max rank estimated and adjusted
• Client patch published and tested on a clean machine
• Refinement mechanics and risks documented for the community

Errtel and Mysterious Stone, well configured, give your server an endgame progression with that satisfying tension of risk and reward. The secret lies in the joint calibration: rank, options, refinement chance, failure behavior, and material source all need to talk to each other. Adjust in cycles, measure the real rates in tests, respect the elemental system's ceiling, and communicate the risks clearly — that way refinement becomes the long-term goal that keeps veterans on your server.

Frequently asked questions