Magic Spring is ok, and potentially provides endless mana for resurrects/spells when you leave a small stack of no-retal enemies (vampires/imps/royal snakes/etc.) alive, but for my warrior game (where rage generation is a non-issue) I didn't find a need to generate endless mana. As such, a fully leveled Mana Accelerator or Calm Rage for boss fights provided me with all my mana needs.

Then again, maybe its just because I used easily resurrectable units in the form of undead and droids.

As such, I still think Phantom is the best since all the classes could abuse it.

I think some of you guys might be misunderstanding the question: It isn't about the most powerful spell, it's the most OVERPOWERED spell.

Phantom and Target I can see. Death Star is strong but not overpowered considering its cost and the fact that you can only cast it once a turn. Yes it does a lot of damage. Fear is overpowered because you can shut down a stack for 4 turns regardless of the size of that stack. With a mage, you can shut down 4 stacks in 2 rounds, effectively allowing you to do whatever you please.

But.. how can something be overpowered if it wasn't worth casting in most of the fights, compared to something that I cast in almost every fight?

If you're playing a Mage, I'd say Phantom. Warrior or Paladin, Fear. The ability of a mage with tier III higher magic to cast a 20 mana Phantom and still cast any regular spell is crazy, especially with summoner 3. All you have to do is max out one creature, ie black knights, with max leadership items, and then Phantom like crazy. Fear is great, but its lack of use vs too many creature types can't compare to the utility of Phantom + Summoner 3 + Higher Magic 3.

You probably play Mage a lot? :)

I play warrior and I don't use fear at all. If I cast fear on one enemy, I only keep one enemy at bay. If I cast Phantom on my Bone Dragons and fly those over to the enemy lines, I practically keep almost all of my enemies at bay, and I get to damage them to boot.

25 mana is not out of reach for a warrior, especially with double rage-generation and mana accelerator/calm rage to convert it to mana.

Like I said, any class could abuse Phantom.

I agree that phantom is still powerful for a war or pal, but with fear lasting 4 turns, you can use it to lock down almost all of a 5 unit low level enemy. At 10 mana, I think it's a much closer call vs the 25 needed for a max phantom for mana-strapped classes. Also, with magic runes being in much shorter supply, it's harder to justify getting summoner 3.

I'm going for stoneskin and phantom. Remove these 2 spells and a lot of tactics would be obliterated.

In my last game I used the Black Knights for the Final part of the game. Resistance went from 52 to 92%, and it boosted defence by 40% which at that time meant around 30 points to defence when mastery was on max.
That means a whopping 92% damage reduction from most physical enemies. An attack on a Black knight with 52% resistance which normally does 1000 dmg will only do 80 dmg on a black knight with Stoneskin on. The two hardest bosses in the game becomes very very easy even without evlin.

Baal is easy on impossible mode = overpowered spell. (and unit)

Phantom should be nerfed for the next game, so that unit skills won't be allowed for the summoned unit. It would still be a good spell for the extra tank and dmg output. OR the mana cost should be greatly increased.
Summoning paladins, green and bone dragons, inqusitors, dryads, demonologists etc for their skills makes it overpowered imo.

I play warrior on Impossible difficulty, and I could definitely say Phantom at 25 mana is definitely more cost effective than Fear at 10 mana. Phantom lasts 3 turns, and you could use the last turn more effectively by just doing a "wait" command. Like I mentioned before, a warrior can only cast one spell, so you could only cast Fear on one enemy at a time. That means on turn 1 you've only locked down one enemy; the rest makes a bee-line for your troops, and that is if you are LUCKY enough to have most/all of your enemies as melee types that have low speed. Turn 2 has only 2 enemies locked down; by this turn, movement 3 melee enemies have reached your troops. That means that they have a chance of causing casualties to your army, making you spend more mana to bring back lost troops.

Fear has 3 disadvantages:
1) It is level dependent, and enemies could still attack equal or lower level units in your army.
2) It doesn't damage the enemies.
3) It controls only one stack of enemies. As you've probably noticed in the later part of the game, you sometimes fight enemies that are distributed into 7+ stacks.

Summoner 3 is nice, but not necessary. If you Phantom tough units the enemies would not be able to even finish off your Phantom, and it would most likely disappear due to the spell's expiry and not due to death. Remember, warrior has double the base leadership gain of a mage.

And before you say that warrior is a mana-strapped class, please first try playing warrior, with a focus on mana accelerator (and calm rage for boss fights), and prepare to be pleasantly surprised. :)

But words are sometimes cheap, so attached is a screenshot of a sample battle of a warrior using Phantom. First turn of the battle here, can you tell me how many enemies are looking to attack and damage my "real" army? :) This enemy type also shows a 4th disadvantage of fear; the enemies I usually want to cast Fear on are range units. But Fear doesn't work on Necromancers (undead), the only ranged unit on the enemy's side.

Um, you do realize that a lot of this is army dependant right? I mean, an army of level 5 units gets a whole lot more out of fear than one with level 3's in it.

Also, lets not compare how well a spell works against an opposing army of only melee units, since a LOT of spells will lock that particular guy down. Also take into account class.

Phantom's strength is based on two things: The leadership of the stack, and the intelligence of the hero. Since warriors have twice the leadership (roughly) of mages, their phantoms (without summoning) are twice the size, before intelligence is considered. Mage has to get a lot of int and other skills to get anywhere near what the warrior gets out of this spell.

Fear on the other hand is a control spell that will lock down a unit from attacking for most of the game. For a smaller army, this can often be more important than doing more damage. It also prevents a hero from casting, if his only stacks are feared. Also, don't compare a single phantom to a single fear, but rather a pair of fears, since a mage can cast it twice. They are both good spells to be sure.

Just because a spell worked great in one particular run-through doesn't mean it is 'overpowered' in all of them, since army makeup, items, and class changes between them.

First game with mage (no-loss), using paladins in a full army, stoneskin+target made it easy, because I also had +20% physical resistance. I was using phantom instead of resurrect.
Second game with warrior (no-buy), mostly vampires, no physical resistance item, but stone skin still halves damage, and that's all it needed.
Third game with paladin (level 1-2), swordsman + cave spiders with stone skin. Also, using dryads + marauders + phantom for infinite money.

Fear is nice too, but it just doesn't compare to stone skin, or phantom for that matter. Slow and Trap are just as nice, but they're all situational.