Needless to say, the one thing that breaks all the rules on a battlefield is magic. Spells and magical items can create almost any condition imaginable, ranging from the merely annoying to the truly catastrophic. We could spend most of this book describing the exact effect of each and every spell and magical item in the game system, but this wouldn't be very practical. Instead, we'll discuss the most common effects that may give DMs trouble.
Wizard Spells[]
The most powerful and effective spells in the AD&D game are found in the hands of wizards. In fantasy role-playing, wizards often dominate battlefields like heavy artillery or airstrikes in modern warfare. Entire battles often hinge on one character's choice of spells and the enemy's attempts to down the wizard before he wreaks havoc on them.
Blink[]
The spell blink works slightly differently in the Player's Option combat system. Roll 1d6; on a 1, the wizard blinks in the very fast phase, on a 2, fast, on a 3 or 4, average, on a 5, slow, and on a 6, very slow. The wizard's blink always occurs first in the phase, before any other actions are resolved.
Darkness, 15' Radius[]
Creatures outside the area of darkness cannot trace a line of fire through the darkness to a target on the other side. Creatures moving in total darkness are reduced to 1/3 their normal move unless they wish to risk stumbling. (Darkness, 15' Radius)
Enlarge[]
A character who grows to eight feet in height becomes size Large; a character who grows to 12 feet in height becomes size Huge. This affects reach, threatening, and moving through smaller figures; see Chapter One. Very large monsters can be made smaller by applying the reverse of this spell. (Enlarge)
Fog Cloud[]
As with darkness, magical fog blocks any lines of fire. Creatures blundering through the fog can easily be ambushed by enemies waiting for them to come into the open; the DM can insist on surprise checks if he deems it appropriate. (Fog Cloud
Hallucinatory Terrain[]
This spell is very dangerous when used to conceal hazardous areas. If the victims do not perceive the illusion, they fall prey to whatever hazards the terrain holds. For example, creatures who run down a hillside believing it to be level ground receive no Dexterity check or saving throw to keep their balance; they automatically fall and roll or slide to the bottom of the hill. (Hallucinatory Terrain)
Haste[]
Creatures under the influence of a haste spell increase their base initiative and weapon speeds by two phases and always win initiative. Their movement rates are doubled, and they gain a second set of attacks in the very slow phase.
Invisibility[]
The best thing to do with an invisible character or monster in a fight is to secretly note its location each round and physically remove the figure from the board. Do yourself a favor and don't run combats with invisible figures on both sides. (Invisibility)
Jump[]
The creature empowered by this spell can actually leap over Man-sized targets without provoking an attack of opportunity. In addition, if the jumper wins initiative, he can make a half-move action to leap away after he attacks an adjacent figure, whether or not he is threatened by his enemy. (Jump)
Pyrotechnics[]
The smoke effect of this spell blocks lines of sight and hinders missile fire just like magical mists or fogs. (Pyrotechnics)
Shocking Grasp[]
At the DM's option, creatures in metal armor may be considered AC 10 versus the wizard's touch. Only Dexterity and magical adjustments apply. (Shocking Grasp)
Slow[]
Creatures affected by a slow spell automatically lose initiative and reduce their base initiative and weapon speeds by two phases. As noted in the spell description, their movement rates and attack rates are halved.
Priest Spells[]
Few priest spells in the Player's Handbook that do not duplicate wizard's spells actually affect the battlefield to any significant degree. However, the Tome of Magic includes a number of priest spells in the sphere of war designed for the battlefield.
Air Walk[]
Creatures affected by an air walk spell move and fight as if they were on solid ground as opposed to engaging in true aerial combat. They threaten squares in front of them and can guard against the attacks of other flying creatures, gaining the advantages of that combat action.
Obscurement[]
Like magical fog, obscurement blocks lines of sight through the affected area, screening creatures in or behind the mists from most missile attacks.
Magical Items[]
There are hundreds of magical items that can create various effects on the battlefield. The exact results of a magical item's use are left to the DM's discretion, but here are some general guidelines on some specific items. In cases where a magical item duplicates a spell effect, refer the spell sections.
Potion of Growth[]
Characters may easily change size by imbibing a potion of growth; they gain the advantages of extended reach and size bonuses in overbearing or overruns as normal for monsters of that size.
Potion of Invulnerability[]
The imbiber can still be knocked down, grappled, or overborne by creatures he is otherwise immune to. (Potion of Invulnerability)
Apparatus of Kwalish[]
The mechanical claw attacks of the apparatus act in the slow phase of initiative. (Apparatus of Kwalish)
Boots of Speed[]
The Armor Class bonus applies when the character chooses a half-move or full-move combat action. Going toe-to-toe in a melee doesn't allow the wearer of the boots to take advantage of their defensive properties, although he can always use the extra movement. (Boots of Speed)
Boots of Striding and Springing[]
If the wearer strikes before his enemy because of a better action speed or because he won initiative, he may spring away as described in the DMG without provoking an attack of opportunity. The +1 AC bonus applies all the time, even when the user is mired in a stationary slugging match. (Boots of Striding and Springing)
Crossbow of Accuracy[]
Although the weapon treats all shots as short range, it still has medium and long ranges for purposes of armor penetration. See crossbows in Chapter Seven: Weapons and Armor. (Crossbow of Accuracy)
Scimitar of Speed[]
The scimitar of speed is very fast, and its wielder always wins initiative if he declares a combat action that involves an attack with the weapon.
Short Sword of Quickness[]
See scimitar of speed, above. If two such weapons are involved in a single battle, their strikes are considered to be simultaneous. (Sword of Quickness)
Sword of Sharpness[]
The magical properties of sharpness override the normal critical hit procedure. It is still possible to achieve a normal critical hit by rolling an 18 or 19, even if it doesn't quite activate the sharpness properties. If a limb is severed, consider the injury to be a critical one of the appropriate sort—Chapter Six details the unpleasant effects of losing limbs.
Vorpal Sword[]
As with the sword of sharpness, the properties of a vorpal blade override the critical hit procedure. If the wielder rolls an 18 or higher that meets the criteria for a critical hit without invoking the vorpal power, a normal critical hit results.