Wizards - Baldur's Gate 1 Beginner's Guide
Wizards are one of if not the most over powered class in all of Dungeons and Dragons. The higher in level they get the more godlike they become and in Baldur's Gate it's no different. You'll typically always want a Wizard in your party both for the buffs that they will provide the rest of your group as well as the insane amount of CC and damage that they can put out.
I would say that from levels 1 - 5 Wizards are not that powerful and for the most part Fighters and all other melee/ranged will outshine them. It isn't until you start learning more powerful spells such as Haste and Fireball that Wizards really start to shine and show their true value. Haste especially is probably the best Wizard buff in the entire game since it will double the amount of attacks you can perform during each round and is a party wide buff.
Eventually towards the end of Baldur's Gate 1 your Fighters and other melee become nothing more than speed bumps to slow enemies down and prevent them from reaching your casters. You'll be depending largely on your casters to dish out the majority of the damage each fight.
To help you understand which Wizards spells are worth using and which are not I have included a complete list of all the spells I believe are worth using. I know this is a bit much which is why I also made an abridged version of this same list which tells you more or less the spells I choose to memorize for each spell level.
(Level 1) Magic Missile & Identify
(Level 2) Mirror Image or Blur and Web if desired
(Level 3) Haste, Fireball or Skull Trap, Remove Magic
(Level 4) Stoneskin, Minor Sequencer, Greater Malison
(Level 5) Animate Dead, Greater Malison, Cloudkill, Chaos, Breach, Spell Immunity
Below is a complete list of all Wizard spells that I think are worth using in Baldur's Gate 1. The list you see below is slightly different in my Baldur's Gate 2 Wizard Guide because some spells got nerfed or are just plain flat out no longer useful when new spells are added. In the BG2 guide I am a lot more selective and strict on what I included, I include mostly the best spells rather than having a lot of semi-decent ones clogging up the list.
Most Notable Wizard Spells:
(Level 1) Magic Missile: One of the best spells in a Mage's arsenal; this spell is difficult to resist and deals good damage. Typically I always keep my Level 1 spell slots filled with mostly Magic Missile and some Identify.
(Level 1) Blindness: This spell works both as crowd control and as a debuff; when successful it'll decrease the targets Attack Rolls and Armor Class by -4. Additionally, it has a hidden effect that can prevent enemies from attacking at all which you can read more about on the wiki.
(Level 1) Charm Person: You can use this spell in and out of combat. Many NPCs will have hidden dialogue if you Charm them and talk to them in BG1. Inside of combat you can charm an enemy then turn him on his own allies to literally turn the tides in your favor.
(Level 1) Grease: A low level CC spell that I don't really like; it's like a lesser version of Web. It's an AoE that slows enemies that fail to make a Saving Throw. This spell is praised by many though so I included it in the list.
(Level 1) Spook: Spook is a single target fear spell. This CC is extremely good in BG1 but we're faced with the same problem we had with Grease... Is it better than Magic Missile? No is my answer.
(Level 1) Identify: Last but not least we have the only level 1 spell that can compete with Magic Missile, Identify. This spell allows you to identify magical equipment and is a spell that you'll typically always want to keep memorized on one of your casters.
(Level 2) Melf's Acid Arrow (BG1): This is probably the highest damage Level 2 spell that you can get as a Wizard. The arrow deals 2d4 Acid Damage and then also places a DoT on the target that deals 2d4 Acid Damage for a number of rounds depending on the level of the Wizard.
(Level 2) Web: As the name of the spell suggests, using Web will create a giant spider web on the ground which will immobilize any targets that enter into it. This CC will work on hostiles as well as your own party members so you have to use it carefully. For more information about how to effectively use Web check out my BG1 Beginner's Guide Combat Strategies.
(Level 2) Blur: Blur is a self only defensive buff that is available to Wizards. While under the effects of Blur all attack rolls against you will suffer from a -3 penalty and you'll also gain a +1 bonus to all Saving Throws. Typically all Wizards I use will have either Blur or Mirror image memorized in a couple of slots.
(Level 2) Invisibility: This spell makes your character invisible until you attack or perform a specific action. I recommend you check the wiki as there are quite a few different skills you can use while invisible that will not break it. Unlike the Improved Invisibility Level 4 spell this one provides no benefits at all during combat. One of the biggest benefits to Invisibility is using it on a Thief and having them scout a dungeon and disarm all of the traps.
(Level 2) Detect Invisibility: When you are playing on Story, Easy or Normal this spell won't be that effective. For the most part no one will use stealth and any enemies that do can't one shot you. However when you start ramping the game up in difficulty you'll want a spell like Detect Invisibility to get Thiefs out of stealth.
(Level 2) Mirror Image: Mirror Image is a self only defensive buff that is available to Wizards. Casting this spell will create duplicates of your Wizard providing you with protection as typically one of your illusions will be hit with attacks instead of you. Each time an illusion is damaged it disappears. Blur and Mirror Image are the 2 most useful Level 2 spells in my opinion.
(Level 2) Horror: This is the AoE version of Spook which fears an entire group of enemies. I'm sure one of your characters has been feared before in this game and you've seen how long it lasts and how useful it can be -- well with this spell you can do the same to enemies!
(Level 2) Stinking Cloud (BG1): Another AoE CC spell that will affect both enemy targets as well as your own party members. When using Stinking Cloud any creature caught in the cloud will have to perform a successful Saving Throw, failing to do so will cause them to pass out and become immobilized for 9 seconds. This spell can be combined with Animate Dead (since undead don't breath and aren't affected by this spell) to take out an entire group of enemies.
(Level 3) Fireball: One of the best AoE spells in the game if you're playing on lower difficulties. Throughout almost all of BG1 this spell will completely decimate groups of enemies. However, the more you go up in difficulty and level the more Skull Trap will outshine this spell.
(Level 3) Skull Trap: When used correctly this can be one of the most powerful AoE damage spells in BG1 and in BG2. Skull Trap allows you to place a trap on the field (which doesn't go away when you rest) that explodes and deals 1d6 damage per level of the caster -- with no cap. This spell will not explode until an enemy steps into range of it which means you can stack multiple Skull Traps onto each other then pull an enemy into them and blow them all up. Even better, most enemies will have no resistances to the type of damage Skull Trap does (magical).
(Level 3) Invisibility, 10' Radius: This spell is a lot like Level 2 Invisibility except that it will work on your entire group when you cast it. Aside from all the scenarios you can imagine this spell being useful (like sneaking into a room of enemies to get the jump on them) you can also use this spell to end combat in a worst case scenario. Say you're fighting a tough enemy that can only be damaged with +3 weapons and your 2 chars with +3 weapons just died. Use this invis on your whole group to break combat and give yourself an opportunity to get to safety.
(Level 3) Melf's Minute Meteors: Arguably one of the best spells you can get for Level 3. This spell allows you to conjure essentially a throwing weapon with a massive THAC0 bonus which will deal 1d4+3 each time it hits a target. Each cast of this spell will give you 1 meteor for every level your Wizard is and they last until thrown. The best part about this spell is it will raise your attacks per round to 5, when Improved Haste is active you'll get a total of 10 attacks per round! This is absolutely insane and allows the Wizard to deal some serious damage.
(Level 3) Protection From Fire: Most of the magical damage you'll take in this game is fire damage so having some protection against it is obviously a good idea. The downside of this spell is it's single target only so keep that in mind.
(Level 3) Slow: Slow is an AoE debuff that reduces the movement and attack speed of any enemies hit by it by half. I'd highly recommend this spell when you play on Core Rules or higher since decreasing the amount of incoming damage from enemies is very important. This spell will only take affect on targets that are hostile to the caster; meaning that any members in your party who are in the AoE radius will not be affected.
(Level 3) Spell Thrust: Depending on the difficulty you're playing on this spell will either be very useful or not at all. Essentially all the spell does is it strips all spell protections off of your target if they're below the 5th spell level. You'll be using this spell against many enemy mages that you fight in this game since they're the only ones who can use these protections. However, on most lower difficulties I do not think mages use many spell protections.
(Level 3) Haste: Haste is one of the best spells in the game; Improved Haste is a better but single target only version of this skill. I prefer using Haste for most of BG1 especially when I am using the Animate Dead or Pet strategies. Buffing your entire group + your summoned pets with 1 spell saves you so much time. 10/10 I recommend this spell to everyone.
(Level 3) Hold Person: Hold Person is a very powerful CC spell that is available to both Priests and mages; the biggest downside to this spell is that it only works on humanoids. One extra benefit that I like about this spell is the game's AI will automatically use it during most fights which is equally good and bad depending on your playstyle. For Wizard I would kind of recommend not using Hold Person because you have many other valuable level 3 spells that you have to use.
(Level 3) Remove Magic: Remove Magic is an AoE version of Dispel Magic that will only affect enemies in the targeted area. Some status effects on your own party can be dispelled too but it will not strip away your buffs which makes it loads better than Dispel Magic.
(Level 3) Vampiric Touch: This spell when used will give the caster temporary hitpoints that will last for an ingame hour. Usually it's best to use this spell prior to combat on a summoned creature, some random critter you pass in the world or even on one of your own party members. You can use Vampiric Touch on a party member to get your mage a lot of bonus HP then heal the party member up and proceed as originally planned. All in all it makes a great pre-combat buff.
(Level 3) Flame Arrow: At lower levels this spell is just ok but as you level up every 5th level you'll throw an extra Arrow which will start to drastically increase the amount of damage you can do with this skill. The biggest downside of this skill is that you deal fire damage which is some of the most heavily mitigated damage in the game.
(Level 4) Greater Malison: Essentially what this spell does is it creates an AoE area that applies a -4 penalty to all Saving Throws that hostile creatures make. This spell does not affect party members that are standing the AoE which makes it even better. Arguably you'll want to use this spell as much as possible since it'll make all of your debuffs and spells hit more often and/or deal more damage.
(Level 4) Fireshield (Blue): Fireshield (Blue) is a self only buff that places a shield on the caster that gives 50% Cold Resistance as well as inflicts 1d8+2 cold damage to anyone attacking you in melee range. This skill can be combined with Fireshield (Red) to deal significant damage to enemy melee units.
(Level 4) Fireshield (Red): Fireshield (Red) is a self only buff that places a shield on the caster that gives 50% Fire Resistance as well as influcts 1d8+2 fire damage to anyone attacking you within melee range. Much like with the previous Fireshield, this one can be combined to deal significant damage to all enemy melee units.
(Level 4) Spirit Armor: This spell can be cast on yourself or on any other party member. It'll set their AC to 1 and also provide them with a +3 bonus to Save vs Spell. It's a good spell to use on classes that can't wear good armor and this spell stacks with things like Improved Invisibility, Mirror Image and Blur. Using all of these defensive skills at once will make your character extremely hard to take out.
(Level 4) Stoneskin: Stoneskin is arguably one of the best skills in the entire AD&D ruleset because it makes you immune to physical attacks and lasts for an extremely long time. How this skill works is you will gain a 'stoneskin' for every 2 levels; at level 10 you get 5 skins and at 20 you get 10. What 10 skins means if you can take 10 physical attacks before your Stoneskin wears off. This is the most important buff for you to use in the game, make sure you always have it active.
(Level 4) Minor Sequencer: Another amazing spell, it's difficult to explain how this works (even the spell description is really long) but basically you create a spell gem that contains 2 level 2 spells. It will consume these spells until you rest at which point you'll get them back (and you'll keep the sequencer aka spell gem). At any point in the future you can use the sequenced spells and it'll instantly cast them. One combo that is especially nice is Mirror Image and Blur as both of those spells can save your life if you're getting heavily attacked.
(Level 4) Wizard Eye: This allows you to see through the fog of war. If all you plan to use Wizard Eye for is scouting then it is a waste of a spell slot. However, you can use this spell with summons such as Animate Dead to send them into another room and still issue commands to them. This works too for Wizard abilities like Simulacrum; you can get complete control of this summon and remotely take out an enemy such as a Beholder far away from your actual group.
(Level 4) Improved Invisibility: This spell is like regular Invisibility except it doesn't last as long and it can also be used in combat as well. Any enemies that attack you while under the effects of Improved Invisiblity will suffer a -4 penalty to their attack rolls. Additionally, your character will have a +4 bonus to all Saving Throws.
(Level 4) Secret Word: Unless you're playing on a difficulty harder than Core Rules you probably will never need to use this spell. What this spell does is it dispels one spell protection (below the 8th level) from an enemy; typically in the lower difficulties the only enemies that will use spell protections are bosses.. Specifically caster bosses.
(Level 5) Breach: When you play on Core Rules this spell will start to become very useful; I would argue you can get away with not using it on lower difficulties. What Breach does is it dispels a complete laundry list of combat protections on the enemy, far too many to name here. Once you start playing on harder difficulties you'll have to use this against enemies who have lots of buffs.
(Level 5) Chaos: Essentially this spell is a very buffed up version of Confusion; you can use this on an entire group of enemies and then easily take them out. Depending on what difficulty you're playing on quite a few enemies are susceptible to this.
(Level 5) Cloudkill: This spell deals good poison damage if you stand inside of it and has a chance of instantly taking out weaker enemies or enemies unlucky enough to roll poorly on a Saving Throw. Usually this spell is best used to take out enemy casters from a distance and interrupt their ability to cast spells.
(Level 5) Spell Immunity: When you cast this spell you will be able to make yourself immune to 1 spell from a school of your choosing. For the most part you will be using this spell on higher difficulties to make yourself immune to Abjuration so that you can resist Remove Magic and Dispel Magic against high level enemies like a Lich. Immunity to Alteration will help you avoid Flesh to Stone and Disintegration based attacks like Sphere of Chaos.
(Level 5) Spell Shield: Spell Shield is a self only buff that you will want to use on your mage to protect yourself from other mages. With this buff you'll protect yourself from many different mage spells that strip your defenses from you. Much like all the spells of this type, people on lower difficulties will not need to use this very often. Those of you on higher difficulties know that a mage without his defenses is a dead mage which is why this spell is important.
(Level 5) Animate Dead: Arguably the best summon spell in the entire game since undead get an innate resistance to all physical damage except crushing and an innate resistance to magical damage. The biggest downside of this spell (for a Wizard) is that it is a level 5 spell. Clerics get the same exact spell at level 3 and arguably you should use Animate Dead on them instead of on your Wizard.
(Level 5) Oracle (BG1): This spell is a lesser version of True Sight and it's a spell I don't recommend you take unless you're playing on Core Rules or higher. Essentially all this spell does is let you reveal Thiefs or any other invisible targets on the battlefield. You can get this spell and use it in BG1 which is useful too, in BG2 there are many other useful spells.
(Level 5) Lower Resistance: Lower Resistance lowers the magical resistance of a single target. Useful against powerful Drow or other enemies that have exceptionally high magic resist.
Since we cap out at Level 5 spells in Baldur's Gate 1 that's as far as this page will go. If you'd like to see a complete list of spells which will cover both BG1 and BG2 I recommend you check out my Baldur's Gate 2 Wizard Beginner's Guide. That guide will cover every spell level.