In this episode, three things cause me to start over MC Eternal with a new world:
1) I used Default World Type, instead of the recommended Biomes o' Plenty World Type.
2) That seems to have caused problems with finding a few Fish's Undead Rising mobs I need to finish the Introduction chapter (no Coniferous Forest, for instance).
3) In an attempt to build a couple dozen dimensions with RFTools, to hopefully get those missing dimensions/mobs... I crashed my game a couple times trying to build two apparently problematic dimensions and my world was becoming increasing laggy and unstable.
So, time for a reboot! It will be fun to get off to a faster/better start, now that I am more familiar with the modpack!