One of the most various spellbook,Mordor Spellbook was slightly modified in 3.6,according to the new nazgul system.
However,i have been thinking about changes in MS since 3.3,and i think they are still topical.
Fierceness of the East
Mordor has 2 mass killer spells,namely Barrage and Rain of fire.
Rain of Fire is a power that perfectly fits with the mordor feeling,it well represents the might of the Orodruin,the Mount which was able to destroy the One Ring itself.
It should never be removed.
Barrage,instead,is already present in the Dwarven Spellbook and has no real pertinence with Mordor.
Barrage is so replaced by the new power Fierceness of the East.
This summons 2 young Mumakil.They are smaller(0.75),have no battle towers on them,they haven't Charge ability and have 5000 health only.
Normal Mumakil would be simply too strong,being already effective against units,heroes and buildings alike.
17pp cost.75 seconds duration.6 minutes recharge time.