Ghost Grey Challenge Runs: Nuzlocke Rules and Level Caps

Ghost Grey is a good Nuzlocke and a bad blind Nuzlocke. The hack's own data does not document a challenge mode, a difficulty setting or a level cap -- what it does give you is every boss's actual team, and that is the hard part of building rules that hold up.

This page is a ruleset you can actually follow, plus the numbers behind it. Every level below is read from the ROM's own trainer tables.

Decide your rules before the first catch. Retrofitting a death rule onto a run you have been playing loosely is how challenge runs quietly stop being challenges.
Turn off the things that remove the difficulty (in-battle healing items, switching after a knockout).
Take the caps below as ceilings, not targets. Being under a cap is normal here; being over one is what makes the run easy.

Level caps that come from the ROM

Caps in progression order, each one the top level of the fight that gates that stage:

When you reach	The fight in the way	Cap
Cerulean City	Maj. Voltage (Shock Badge)	21
Vermilion City	Maj. Voltage again (second Shock Badge)	21
Celidon City	Erika (Plague Badge)	29

Two things about that table:

The caps follow progression, not badge flags. The first badge flag in storage is the Volcano Badge at Seafoam Islands, sitting behind a Lv 65 Murkrow -- so a cap table built from flag numbers would have you fighting a Lv 65 boss as your first badge. Read the badge table in the walkthrough alongside this one.
Two badges have no fight at all. The Famine Badge (Desert Palace) and the Volcano Badge (Seafoam Islands) are found. There is no cap for those stages, so the honest rule is either "cap at the last fight you cleared" or "cap at whatever comes next".

The rules this hack changes

1. A Ghost-type is not a safe switch. In Ghost Grey, Normal-type and Fighting-type moves hit Ghost-types at 1x instead of doing nothing. The vanilla habit -- leave the Ghost in, nothing can touch it -- is wrong here, and it is wrong in both directions: your Ghost does not wall a Normal attacker, and a Ghost-type boss does not shrug off your Normal moves. This is the single most common way a first Nuzlocke death happens. We cover the type chart in the FAQ.

2. There are no EVs, so there is no EV training. Every species' EV yield in the ROM is empty. Levels and IVs are the only dials you have, which makes a Bottle Cap genuinely valuable for a Nuzlocke team: one is sold for 70,000, and the ROM also records a Bottle Cap as a gift in Celidon City.

3. A story step consumes a Pokémon. The post-game asks you to prepare one of your team to be sacrificed, and the game means it. If you are carrying a Nuzlocke into the post-game, budget a slot and decide in advance whether you count it as a death.

4. Encounter supply is a rule choice, not a limit. 83 areas hold wild encounters, and 47 more Pokémon are fixed -- 28 standing statics, 16 gifts and 3 eggs. Decide before you start whether a static or a gift counts as the encounter for its area. If statics do not count, you have well over a hundred chances in a game that starts balancing around Lv 45 and ends at 99, which is generous for a Nuzlocke and the main lever you have over difficulty.

5. Stones are not the wall you might expect. All six of the hack's evolution stones (Abyss, Avarice, Dusk, Harvest, Moon and Sun) are sold or given before the post-game -- Saffron City sells five of them, and Moon Stone has four separate gift or overworld sites. The Northern Cave hides one of each later, but you do not have to wait for it. Check the evolution guide before you build a team around a stone evolution.

6. HMs are on the critical path and worth budgeting. There are seven obtainable HMs, and Cut is Steel-typed in this hack rather than Normal. HM08 exists in the data with no location, exactly like TM25 has no site, so do not plan around a move the game never hands you.

A ruleset that fits this game

Hardcore Nuzlocke, adapted. This is the version we would recommend for a first challenge run, and it is written so you can tick the rules off before you start:

One catch per area, first encounter only. Decide now whether a static or a gift counts as that area's encounter.
Faint is dead. Box it, do not use it.
Caps from the table above. If a team member is over the cap, box it until you clear the stage.
No healing items in battle, and no switching after a knockout. Ghost Grey does not enforce either, so this is the honour-system part.
Dupes clause on, generously. The dex is rebuilt -- 291 species, 132 of them original to the hack -- so there is no scarcity argument for keeping a duplicate.
Treat Ghost-types as neutral, not immune. Build a defensive core that actually resists things instead of parking a Ghost in front of Normal attackers.
Budget the sacrifice if you are playing into the post-game.

If you want it harder, the honest levers in this hack are the caps (drop one level under each) and the static rule (statics do not count), not arbitrary restrictions like "no Ghost-types", which would fight the game's own type design.

Where challenge runs actually end

The jump at Seafoam Islands. The fifth badge's leader tops out at Lv 45, and the Volcano Badge on the Seafoam floor is guarded by a Lv 65 Murkrow. That is the biggest single jump in the game before the endgame, and it is not a badge fight, so a cap table on its own will not warn you.
The endgame pair. The last two bosses are stored at Lv 95 to 99. Leaving the League at Lv 70 with a Nuzlocke team means treating the post-game as its own levelling campaign rather than an epilogue.
The point of no return. Before the final yes/no the game warns you that you cannot return to the world. Finish your shopping, evolutions and Bottle Cap work before that prompt.
Cut is required early. HM01 is a gate item as well as a Steel-typed move, so a run that skips it stalls inside the first hour.
The sacrifice. The one mandatory loss in the game, and the only one a Nuzlocke ruleset has to absorb rather than avoid.

What this page cannot tell you

Whether the game has a built-in challenge mode. Nothing in the item, trainer or flag data documents a Nuzlocke or difficulty setting, and a binary hack's menus are not readable from the published data. So we do not claim either way -- if you find one, it changes nothing about the caps above.
Which fights are skippable. The ROM does not mark story gates, so we cannot compute a route that dodges an optional boss.
What the sacrifice means for your save. The game's flags do not record it as a death, and whether you count it as one is your rule.
Which variant of the Hope Badge fight you meet, and why. That badge's script holds three variants of one battle -- three rows of the same rival, each topping out at Lv 65 -- and calls one of them based on a story variable. The cap is 65 on every branch; which version you land on is the game's business, not the number's.