I do not see much point to this spell ... Let me explain.
Terror of Darkness - Level 33
Mana: 20
Hate position: +1
Hate added: 200
Terror of Shadows - Level 42
Mana: 40
Hate position: +1
Hate added: 400
So we double the mana cost for twice the hate. It sounds great in theory, but to be honest at this level our primary focus is going to be leveling, and we would only cast this in groups (for obvious reasons). The level 33 version, cast the instant after we land Clinging Darkness (hammer that button) is more than enough threat. Doubling the mana cost on extra threat at this level is pointless.
Skip this spell and stick with the level 33 version until level 53 when you can pick up Terror of Death.
Terror of Death - Level 53
Mana: 45
Hate position: +1
Hate added: 450