James McMurray said:
Teleport is really a game changer. However, that doesn't qualify it for broken status. I have known some DMs that would retre characters once they reached the ability to cast teleport though, because they couldn't handle a game without long journeys to reach goals.
I wouldn't call teleport broken either. It just needs some changes. Most games I have played in put setting limitations on the spell. (In my Dark Sun 3e game I ruled that Teleport opened a Stargate-like wormhole through The Gray and there was a chance equal to the spell level on d100 that some denizens of The Gray get caught in the spell and arrive with the teleporters.
Giving the spell a range (5miles/lvl is what I use) and adding rudimentary teleport defenses also tends to control the spell.
Really busted spells include (many of these were mentioned already):
My most wanted three: Harm, Haste, Timestop.
Plus two other repeat offenders:
True Seeing - defeats almost ALL illusions and a fair number of transmutations and it is only a 5th lvl spell). This spell should be higher level (I'd say 7th or 8th level myself) or cut down substantially, or given a save.
Shadow Magic spells - every last stinking one of these spells is broken. They were broken in earlier editions and they have never been fixed. Have the designers EVER thought about how little logical sense these spells make? The quasi-real concept makes no sense and generates too many rules problems.
For example, if you cast a Shadow Magic fireball that is 20% real, what does that do to a fire giant? The fire giant is fighting an illusionist that he knows does not know fireball. If the giant believes it is real (and fails his save to desbelieve) he takes no damage because it is fire, yet if he sees it for what it really is (and succeeds at his save) he takes damage because it is not fire. This generates the net effect of the giant being worse off for making a saving throw. What if the fireball was instead cast into a warehouse filled with lamp-oil? The oil can't believe in the fire.
What is a shadow-conjured wall that is x% real? Does that mean x% as thick, x% as many hp or only real x% of the time. What happens if you fire a catapult at that shadow conjured wall? The stone cannot believe in the wall.
What about casting a shadow-lightning bolt at an iron golem? The golem is immune to all spells that aren't one of the specific spells in its description. A golem would normally be slowed by a lightning bolt, but this is not actual lightning, it is shadow electricity that is only x% real? What does it do?
Some others I am not fond of but aren't really broken:
Teleport: (see above)
Delay Poison: This spell should be called Immunity to Poison it is so powerful. It really needs a shorter duration. (10min/lvl)
Greater Magic Weapon: This spell really also needs a shorter duration. (10min/lvl)
Simulacrum: This spell is very powerful. First of all it should not be shadow magic, it should be necromancy. Secondly, the spell needs a higher XP cost. I'd say 1000 xp per HD of the creature you are duplicating. I don't think the designers realized what you can do with this spell. I must admit I didn't either until one of my players started using it for intelligence gathering about foes who got away from them. They would make cheap simulacra of the person and gain roughly 50% of the knowledge that that person knew including what high level spells he knows. They would then make a couple of simulacra of the person to minimize the chance that they were missing information. Not only did it give them intel on what their foe could do, but it could teach the PC wizards spells that the might not be able to get normally. I don't think this spell should be banned, I do think it is way to cheap.
Awaken: This spell is also too cheap. Tie the xp cost to the HD of the creature you are awakening.
Telekinesis: I house-ruled that Telekineses can grasp and throw objects like a single hand. This prevents the "barrel of shuriken" problem. Honestly the spell needs an additional fix that ties it to an actual strength rating. You can then tie the spell's damage to that strength rating for the purposes of blows that it can inflict, like any other weapon.
Tzarevitch