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About this mod

A fix for an engine bug which affects all chance-based creature spawns.

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Creature Spawn Chance Fix


This is a comprehensive fix for a known bug relating to creature spawn chances. The game only rolls once for spawn chance when a cell is loaded, meaning that all creature spawn points within a cell are linked to that one roll. In effect, this means that all chanced spawn points within a cell will either spawn a creature or not. In other words, it's all or nothing.

This mod implements a workaround for the above issue. Now all spawn points will roll independently of one another, as intended. The base game and Shivering Isles is covered; no other DLC uses chanced spawns.

An example of the bug and fix is given below, in case my description doesn't make much sense.
  • A cell contains three creatures with a 75% chance of spawning, i.e. a 25% chance of not spawning.
  • In vanilla, you enter the cell: the game rolls once on 1 to 100, and the outcome is 85. All creature spawns are based of this roll, and since 85 is greater than 75, no creatures spawn.
  • With this fix, you enter the same cell: the game will 'roll' three times, once for each of the three spawns. The outcomes are 85, 17, and 54, so one creature doesn't spawn, and the other two do.

How it Works

This bug and the workaround to fix it have been known for a long time—it is actually included in some of the old overhaul mods like OOO. However, to my knowledge, no-one has ever provided a standalone fix, probably due to the time-consuming and tedious task of manually editing all the chanced creature leveled lists. I, on the other hand, had a spare hour, so I thought I might as well. Fix it once, and it's fixed forever.

The "Chance None" for all chance-based creature spawns has been set to 0. Instead, the creature leveled lists are weighted using a dummy null spawn, which doesn't produce a creature. For example, a 75%-chance list is weighted in a 3:1 ratio using three entries for the 100%-chance list for the same creature spawn, and one entry for the the dummy spawn. A 50% list is weighted 1:1, and a 25% list is 1:3. There are no other chances used in Oblivion. The devs of Fallout: New Vegas actually used this same method in that game for creature spawns, and it actually references Oblivion in its editor ID.

Optional Extra File

I don't know what the deal is with this one. There are six leveled creature records in the Oblivion master file which have "Chance None" values of 128, which only shows in TES4Edit. This seems to me to be a flag bitmask. On opening the record in the Construction Set, the "Calculate from all levels <= player's level" flag is automatically added. This makes me think that the flag was meant to be set on these leveled lists, but the data somehow got moved to the wrong field (or something like that, I've never come across this before).

This optional includes just this correction, and should be loaded high up in your load order. The effect is minor: three of the six leveled lists are unused, two are used only once, and the final one has 10 placements within the Kvatch castle. You're basically using it for that last list, which means that the spawns in Castle Kvatch will be more diverse at higher levels.


Standard installation procedure: add the file to your data folder and check in the game launcher or your mod manager of choice.

Load the main file as low down as possible—even after you're bashed patch.

Do not include the main file in your bashed patch in any way.

The optional flag fix file should be loaded higher up, before any mods which edit leveled creatures, and the change can be merged into your bashed patch.


Just uncheck the mod. Uninstalling this mod will have no permanent effects on your save game.


This mod edits a lot of creature leveled lists, but it should be compatible with everything as long as you follow the load order advice given in the Installation section above.

This is because I have nested the untouched 100%-chance lists inside the chance-based lists, which means that any mod which changes the former will automatically have their changes applied to the chance-based lists. If you load this up in TES4Edit, you will see conflicts with your other mods. These are necessary for it to work, but rest assured that the other mod's changes to leveled creatures will still take effect.


This mod actually makes the process of creating overhaul-style mods easier, as it significantly cuts down the number of leveled creature lists which a modder needs to edit if he is overhauling leveled creatures. This is because he now only needs to edit the 100%-chance lists, and none of the chance-based ones. I may even include this in a later version of Ascension for this reason.

As such, I am providing this as an open resource for anyone who wishes to use it in their release. No need to ask me. Please just make sure to credit and link back here in some form.

My Mods

I spend a lot of time creating and supporting my mods, so any donations are gratefully received.