Betweenlands version:

The Betweenlands v3.5.6

Forge version:

forge-14.23.5.2847

Singleplayer or Multiplayer:

Multiplayer Vanilla (I think? I'm not familiar with Thermos, Sponge, etc.)

Installed mods:

Pack: https://www.curseforge.com/minecraft/modpacks/creaturely-craft/
List: https://pastebin.com/KjJWbAhw

Description of the problem

How to reproduce:

1. Create a world.
2. Enter the Betweenlands
3. Explore for an extended period of time and see which mobs end up spawning.

Expected result:

To see all of the mobs I'd seen in previous playthroughs that are in the mod.

Actual result:

I have spent quite some time exploring the Betweenlands dimension on my current world. If I were to estimate, I've explored for multiple hours at a time over the past 4-5 real life days, covering significant portions of the Betweenlands map, in all Betweenlands biomes. I've played the mod many times in the past, and have never encountered this issue, which is: When looking for mobs, I see plenty of hostile creatures, lurkers, and mire snails, but I have not seen a single spawn of the following mobs:
Greebling
Sporeling
Root Sprite
Gecko
Harlequin Toad

Generally, I do anticipate some of these mobs being less common than others, but by now in past playthroughs I definitely would have seen at least one spawn of all of them, if not multiple. And the fact that I have seen zero geckos is particularly strange.

To my knowledge, I haven't used any mods that alter the world generation or mobs spawning of the Betweenlands--only the overworld. And I have double- and triple- and quadruple-checked that I haven't changed anything in the Betweenlands configs that could cause this; I don't believe I've changed anything at all.

Thank you so much for reading. I did my best to provide the information requested, but I'm still learning the ropes of adequately reporting issues, so please know if there's any other information I might provide, I'm more than happy to do it.

Hmmm... I can't reproduce this. There's many of each of these mobs in my worlds.

If you are in a server, might your server properties have its spawn-animals flag in server.properties set to false?

Unfortunately, that isn't it. Spawn-animals isn't set to false, and all other animals spawn fine from other mods (including dimensional mods like Aether: Legacy).

I see you have "No Mob Spawning on Trees" installed. Could be the case that that mod interferes with mob spawning. Sporelings and Root Sprites for example only spawn on wood and mushroom blocks which previously mentioned mod apparently disables (by default).
Maybe try temporarily removing that mod to check if that fixes your problem.

Thanks for your recommendation! I've done as suggested and removed the "No Mobs Spawning on Trees" mod. Other mods removed: OTG, VanillaVistas, and Shamanism. I also reset the Betweenlands dimension for fresh exploration.

Unfortunately, I still haven't seen any of the aforementioned mobs. Geckos in particular are strange to see missing, as usually they spawn very frequently.

Sure thing! I'll do some testing and get back to you.

Hm ok. You said you've previously played the mod and had no problem, so I guess it's still caused by some other mod in your mod pack. You'll have to find out which mod (or combination) causes the issue and then we can look into it.

Strangely, I could not get the issue to repeat in singleplayer, no matter which mods I paired it with. It only seems to happen in multiplayer, despite server settings not disabling any kind of spawning. I'm not sure what could be happening. Unfortunately, I'm not able to test per mod on multiplayer because I already have a pack/world running for more players than just myself. I understand if this means the issue can't be resolved.

What kind of server software are you using? Sponge, Thermos, etc. type of servers are known to sometimes cause some mob spanwing to not work

Ah, I’m not using anything like that, just a normal server with Forge

As it turns out there is indeed a bug that causes Harlequin Toads to not spawn properly. The other mobs you mentioned spawn just fine though.

I'm having the exact same problem, but in single player. No passive mobs are spawning. At first there were no mobs spawning but I removed the custom mob spawn mod from my load order and after that hostile and neutral mobs started spawning.