“There!” Locklar shouted, pointing at the robed mage they had pursued the day before but lost in the maze of alleyways in the Old Quarter.
Mortigan looked and was dismayed to see the bearded man gesturing at his comrade. He recognized the pattern and was not surprised to see Locklar suddenly frozen in place, completely motionless. The bearded magician whirled and disappeared into a dark alleyway between two buildings.
Quickly, Mortigan called the holding spell to mind and began casting it, making a few minor changes at the appropriate points. He finished and gestured at Locklar. The fighter shook his head.
“I really, really, hate that son of a goblin,” he muttered.
Countering a spell which is already in effect can be attempted by casting a “counterspell” of the same spell at the same target or target point. Base chance for success is 6-in-12, with +1 or -1 for every level of difference between the caster and the counterer. Successful counterspells end the target spell immediately, though indirect effects already applied are not undone.
Instant and permanent spells cannot be countered. Counterspells can only be cast to counter the exact same spell, not different spells with similar effects, though different classes can counter spells of the same name. A counterspell cannot be used as a reversed version of the spell and a failed counterspell has no other effect.
This is basically a narrow version of dispel magic which affects only spells with limited durations. Rather than being a separate spell, it consists of casting a counter version of the spell in question. Thus, a first level magic-user could attempt to counter a charm person spell if he knows it by casting charm person’s counterspell.
Regarding the indirect effects, a control weather spell that flattens a building with a tornado or dumps six inches of snow onto a meadow could be countered and the skies would return to normal, but the building would still be demolished and the snow would still be there.
Spells like polymorph other would still require the spell dispel magic because polymorph other is permanent. Continual light could not be countered, because it too is permanent; continual darkness would still cancel it as normal, though, as that is a specific function of that spell.