Some of the most common special and magical attack forms are described here.

Some monsters exude powerful acid that can dissolve flesh and armour. On a successful attack, acid sticks to the victim’s flesh and inflicts automatic damage each round until it is washed off.
Washing off: Water or wine suffice.
Armour: Some acid dissolves armour after a certain duration of contact.

An attack whereby a large monster rushes towards an opponent and makes a melee attack. The momentum of the charge causes the attack’s damage to be doubled.
Clear run: A charge requires a clear run of at least 20 yards. Charges are not usually possible in dense terrain types: broken, forest, jungle, mountain, swamp.
Bracing: Weapons with the Brace quality can be braced against charge attacks, inflicting double damage on the charging monster on a successful hit.

A magical ability that confuses a victim, causing them to obey the monster.
Effects: A charmed victim cannot make any decisions on their own. They cannot attack the monster or attempt in any way to do it harm. They obey simple commands from the monster (if understood), and otherwise try to defend the monster. The victim is too befuddled to cast spells or use magic items.
Breaking: A charm can be broken by killing the monster or by unravelling the magic (e.g. with dispel magic).

Some monsters have special attack forms that inflict damage automatically (without an attack roll) every round following a successful hit. For example, some monsters can latch onto a victim and drain blood each round, while others can crush a victim in a constricting grasp.
Escaping: Generally the automatic damage only ends when the monster is killed.

Certain powerful undead monsters have the greatly feared ability to drain victims’ life energy, usually without a saving throw. Characters lose experience levels and XP, and monsters lose Hit Dice.
Effects: All benefits of the drained levels are lost. The character’s game stats (e.g. saving throws, attack values, spells memorised, etc.) must be updated. For each level drained, the character loses 1 Hit Die worth of hit points. Their maximum hp are reduced by the same amount.
Example: A 6th level cleric drained of two levels would become 4th level and would lose 2d6 hp (or the hp gained when achieving 5th and 6th levels, if recorded). They would also lose the ability to cast 3rd and 4th level spells and to turn undead of 6 or more HD.
Level 0: A victim drained of all levels or Hit Dice dies.
Restoring: Drained levels can only be restored by regaining XP.

A special attack that freezes a victim in place without killing them. The victim retains full awareness of their surroundings, but cannot speak or move until the paralysis ends. Once a paralysis effect ends, the victim regains the ability to move, with no lasting side-effects.

Poisoned or venomous attacks are a deadly risk to characters of all levels. Most poisons kill the victim on a failed save.

When using their bite attack, monsters with exceptionally large mouths have a chance of swallowing the victim whole. A victim is swallowed if the bite attack roll is a natural 20. Some very large creatures also swallow on lower values (e.g. 18, 19, or 20) or if their attack roll exceeds the target number by a certain amount.
Digestion: A swallowed victim automatically suffers a certain amount of damage every round until they die or the swallowing monster is killed. If the victim dies, their body is completely digested and unrecoverable in 6 turns.
Attacking from inside: A swallowed victim can attack the monster from the inside, using a sharp weapon. Such attacks suffer a –4 attack roll penalty.

A dive attack used by some large flying monsters. Swoop may only be used on an unaware (i.e. surprised) victim. A successful swoop inflicts double damage.
Grasp: Additionally, on an attack roll of 18 or more, the monster can grab and carry away the victim (if of appropriate size).

An attack whereby a large monster or large herd of animals uses its great weight to crush a smaller opponent. Trampling attacks gain a +4 attack roll bonus versus a human-sized or smaller target.
Chance of trampling: Creatures able to trample generally have a 3-in-4 chance of trampling each round (1-in-4 chance of using a different form of attack).