I was just trying to get into this mod now, and I'm stuck on getting spirits. As far as I understand it, killing mobs with the scythe should drop spirits, right? Because I have not gotten a single spirit drop so far.

Could this be some cross-mod incompatibility? I know there are lots of other mob-changing mods on this server, but I don't feel like having other mods installed should ever break stuff in this way.

If you're on the latest latest version you should be fine, there was a bug in some old version where mobs refused to drop spirits.

I can definitely confirm that I am on version 0.3.0.

Not sure what to test this with other than to take out mod for mod and create new worlds and wait for forge to load until I can identify the cause. So far I can say that ghasts seed to drop spirits, but everything else I've tested with does not.

Rlly weird, I'll be closing the issue since spirit drops got quite an internal redo in the indev version, it's a json based system now. If the issue persists past the update then feel free to reopen.

Seems the issue lies in this mod. Not sure which side is responsible but having had issues with that other mod before I'd assume you're fine.

Edit: You're definitely fine.
Relevant log from their discord:

03:57] User1: ok so the MHA mod actually deletes nearby entities when hitting a mob
[03:58] User1: can easily test this with arrows stuck in walls
[04:28] Dev1: it still does that?
[04:28] Dev1: huh... i thought we fixed that ages ago
[04:29] Dev1: @Dev2 oi thought we fixed it
[04:29] Dev2: ?
[04:29] Dev1: entities still gets deleted when you hit a mob with our mod
[04:29] Dev2: Wdym
[04:30] Dev1: remember back when we found out that when we hit mobs
[04:30] Dev1: they dont drop items
[04:30] Dev1: cause they instantly get deleted?
...
[04:33] Dev2: It might think the item is a a projectile
[04:33] User1: only have seen that issue with certain entities from malum and arrows
[04:33] Dev2: There’s a system we’re nearby projectiles get deleted when the entity gets hit
[04:33] Dev2: To stop duplication and lingering projectiles
[04:34] Dev2: But it shouldn’t affect items
[04:34] User1: ah yes that will be it
[04:34] Dev2: Unless the drops from your mod count as projectiles