Oh-kay... I think I managed to fix it all. The mod doesn't even hint at the existence of a unit, which in fact is present - the Forsaken Book transforms all Giants into Taus Clasans (Santa Claus) who spawn Christmas trees, toy soldiers (allied troops) and gifts (chests, pretty much like the pet dragon's ability, also include Christmas toys in addition to their original contents).
Hmm, I'm beginning to see why it was disabled. Taus Clasan is supposed to have a healing aura, which doesn't work - but it is a fun unit nonetheless.
A lot of fun indeed, as you can see from the screens
