Following #72 getting fixed, I (dev of Regrowth - the pack mentioned in that issue) have been unable to get the direwolves to spawn under normal mob rules as they now seem to be limited to spawning on grass blocks (none of which exist in the world in Regrowth) under full light, even when using the Biometweaker mod to register them to spawn as type "MONSTER".
Would it be possible to have a config option to alter this behaviour slightly and allow them to spawn under regular mob rules (any block, low light levels) so they can once again be one of the most threatening creatures to stalk the wasteland?