RewardSpell
Spell that is shown to be casted on quest completion in the quest log. Note that this spell will NOT be casted if RewardSpellCast is non-zero. The spell in the other field will be casted instead, in which case the spell here only serves as the visual in the quest log.
RewardSpellCast
Spell that will always be casted at player when completing the quest. This can be learn spell and player learned some spell in result, or buff spell, for example. If this field is non-zero then this spell will ALWAYS be casted and the spell in RewardSpell will not.