Type: Summoning
Strategy: Letting more and more undead be summoned with each level, this spell becomes quite powerful, especially when used with hindrance spells. Since skeletons are immune to most spells like confusion and stinking cloud, it is a good idea to cast any of those hindrance spells and move in with the skeletons, while picking off any remaining enemies with long-range weaponry. Skeletons are particularly good against mind flayers, since they are not affected by this spell.
Importance: High
Type: Dispel
Strategy: Taking care of all specific and combat protection spells, breach is quite useful. Destroying spells like mantle, stoneskin, and absolute immunity, this spell will be of particular help in any battle against a powerful mage. Cast it on a protected mage and watch as his protection defenses disappear.
Importance: High
Type: Hindrance
Strategy: The effects of this spell are exactly the same as confusion. The only difference is that enemies of level 5 or higher, which is nearly all Baldur's Gate II enemies, will get a save versus the spell at -4 instead of the spell resistance being wisdom-based. The end result is that this spell will work better against higher-level enemies. However, it still will be resisted most of the time. Of the two, this one is definitely the one to use if you must.
Importance: Low
Type: Area damage
Strategy: Dealing a small amount of damage each round to every creature in the spell's 20-foot radius, this spell can end up doing wonders when used strategically. For example, cast web away from the party as described previously in this guide. Then, cast cloudkill and watch as the helpless enemies take damage while they are held in place. Cloudkill will work just as well with any movement-hindering spell.
Importance: Moderate
Type: Area damage
Strategy: Dealing more damage as you level up, this spell becomes a true powerhouse. Since the direction of the cone is targetable, this spell is inherently easier to use than all the other circular radius area damage spells. In fact, this lets you target a group of enemies easily, from a distance, and without fearing for your group. It's definitely worth casting whenever you find yourself up against a group of enemies, and that will be a very frequent occurrence.
Importance: High
Type: Summoning
Strategy: This spell works just like any other summon creature spell, with strategies much the same. The only difference is that elementals can actually turn on their master and attack. So, to avoid that unfortunate occurrence, cast a protection from evil spell on yourself. In this case, the elemental has rather low hit points, so it cannot absorb much damage. Also, it barely helps in a fight, and the casting time makes the actual casting impractical.
Importance: Low
Type: Summoning
Strategy: See conjure lesser air elemental. It's the same, but this time, you summon an earth elemental instead of an air elemental.
Importance: Low
Type: Summoning
Strategy: See conjure lesser air elemental. It's the same, but this time, you summon a fire elemental instead of an air elemental.
Importance: Low
Type: Charm
Strategy: This spell lets the caster gain control of any creature that fails the saving throw. Otherwise, the spell acts strategically much like any other charm spell, such as charm person. In this case, though, the difference is that any creature can be charmed. Also, this spell is resisted much less and works incredibly well against most creatures.
Importance: High
Type: Hindrance
Strategy: Preventing the casting of spells, feeblemind works well when it is not resisted. Since the effect is permanent, if it gets off, you need not worry about magical retaliation from the victim mage. Like any spell often resisted, it is much easier to use when combined with a lower resistance spell.
Importance: Moderate
Type: Hindrance
Strategy: This spell works in the same way as hold person, just for all monsters. This spell is quite helpful, as it will let you attack the creature without retaliation. Though often resisted, the spell if most definitely useful. Again, use a lower resistance spell or greater malison beforehand for a better success.
Importance: Moderate
Type: Hindrance
Strategy: Lowering the target's resistance to magic, this spell is wonderful. The effect is cumulative, so the target's magic resistance can be taken down from anything to zero with enough castings. With no saving throws allowed, this spell will always work and is sure to benefit the chance of every spell being successful afterward. It's a definite must for mage battles. You will run into creatures that will be nearly impossible to cast spells upon. This will save your day.
Importance: Vital
Type: Defense
Strategy: Sending every level 4 spell or lower back to the caster, this spell is a godsend in battles with creatures that cast pesky hold and confuse spells (like umber hulks). Working well in mage battles as well, this spell is useful for any low-level magical encounter.
Importance: Moderate
Type: Summoning
Strategy: Like monster summoning I and II, this spell summons monsters to fight by your side. However, in this case, the monsters have very good amounts of hit points and do real damage. A must for tough battles, these monsters will take the hits, deal the damage, and save your party.
Importance: High
Type: Dispel
Strategy: Dispelling all level 5 and lower illusions in the area, this spell has never done much. We've never encountered a time when this spell should be cast. There are only few times, anyway, when you will run into illusions that must be dispelled.
Importance: Low