Type: Summoning
Strategy: Letting 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, then move in on the skeletons while picking off the remaining enemies with long-range weaponry. Skeletons are particularly good against mind flayers, since they are not affected by their spells.
Importance: High
Type: Missile damage - druid only
Strategy: This spells calls down one bolt of lightning that deals two to eight +1d8 points of damage per turn per level of experience. At higher levels, a very good amount of damage can be done, but it is often resisted. Also, the fact that this spell can only be cast outside makes it nearly impossible to use.
Importance: Low
Type: Cure, heal
Strategy: If a party member is affected by disease, blindness, or deafness, casting this spell will cure him. Since this will happen often, this spell is very useful.
Importance: High
Type: Heal
Strategy: Cast this spell on a hurt party member. This spell heals 14 points of damage. For Baldur's Gate II, that amount is small. However, it is useful to cut down on hours of rest, so if you find no better spells, fill up level 2 with this.
Importance: Low
Type: Dispel
Strategy: Most spell-induced ailments and magic effects can be cured with a cast of dispel magic. Since the level of the caster in relation to the level of the spell being cured is important, have your higher-level characters use this. Though this spell is very important to have around, paladins get some casts of this as a special ability. If you have one in your party, this can relieve some of the stress off the spellcaster.
Importance: High or low, depending on party makeup
Type: Defense
Strategy: Used to protect a door or chest from entry, glyph of warding is of no use in Baldur's Gate II, as NPCs do not touch doors or chests.
Importance: None
Type: Hindrance - druid only
Strategy: This spell freezes one animal-type creature in place, letting you do anything to it without consequence. Early in the game, when the spell is not resisted, it could work wonders against animal enemies, but there are none. Later in the game, when you begin to run into animals of some consequence, its effectiveness tapers off, making it all but useless in Baldur's Gate II.
Importance: Low
Type: Area damage
Strategy: Dealing one to four points of damage per level of the caster to all evil creatures in the area of effect with a save for half, this spell will do tremendous amounts of damage at higher levels. This spell works especially well against the undead, sometimes killing a whole pack in a single casting. Otherwise, your group is easy prey to any pack of evil creatures.
Importance: High
Type: Dispel
Strategy: If your party ever comes under attack from any type of invisible creature, casting this spell will force it back into visibility. However, on your journey, you will rarely face invisible creatures, and when you do, they will become barely visible when they attack you. Unless they have used greater invisibility, you can attack them from there (though your party will attack at a penalty). Also, you can easily cast dispel to rid the creature of the invisibility if needed.
Importance: Low