(Modfest 1.21.1)
https://mclo.gs/9a1qEES

There seems to be a mixin incompatibility with Rods from God's EntityTrackerEntryMixin. I think Neoforge is changing the method parameters of the sendPackets (yarn) method, and the method signature doesn't match anymore.

Minecraft and mod versions are here: https://mclo.gs/uyUSJdQ
Mixin class in question: https://github.com/ekulxam/rods_from_god/blob/e7248686f6c094b489fd87433ff3377217466b9f/src/main/java/survivalblock/rods_from_god/mixin/tungstenrod/EntityTrackerEntryMixin.java