As an object You can count following:
- all conjurations,
- all creatures (including Your Mage),
- all equipments,
- and in some circumstances even enchantments,
As regards Your question about "Harmonize".
You cannot put Harmonize on Mana Crystal. The target "object" of Harmonize must have channeling trait.
So You can place Harmonize on Huggin because as familiar it has channeling and Harmonize will increase its channeling.
Mana Crystal/ Mana Flower give to Mage +1 channeling but it doesn't have channeling itself.
You can also put Harmonize on Your Mage or Spawnpoint.