Can I suggest adding to demon factions, like normal WoC races have, a chain that allows you to turn marauders into forsaken and then into spawn? No reasons other than it being there already for another chaos race I guess

As for Nurgle specifically (my fave race currently) maybe exalted plagubearers into pox riders on skill level 5/6 and normal plague toads into pox riders on tier 9? Riders are available immediately in advanced building cycle, so I don't think it's crazy strong or anything, more just a way to possibly add that cav unit a bit earlier in the first 10/15 turns, while also giving a way to upgrade toads into something stronger once you level them up high

Same would go for rot flies into plague drones (maybe around level 6) and then into death heads, which are tier above, at maybe rank 4? This would help with people skipping both of those units and just waiting for death heads cause they are superior in every way, aside maybe from upkeep. Could also make them into an alternative upgrade for exalted plague bearers, maybe tier 3/4 (since relatively similar cost, plague drones being just 25 more expensive)

Aside from that, thank you A LOT for making this mod, it really is fun to play, especially for factions that take long to get to tier 5, it's a must-have for me and my friends now