Dispel

From NWNWiki

Dispelling is an attempt to remove existing spell effects on a creature or from an area of effect. This usually involves dispel magic or a related spell (lesser dispel, greater dispelling, and Mordenkainen's disjunction), but other sources of dispelling exist. Generally, if a dispel is targeted on a single creature, then it will attempt to remove all spell effects from that creature, but if used as an area of effect, then it will attempt to remove all spells with an overlapping area of effect as well as one or two effects from each creature in the area.

Typically, only spells (and feats that duplicate spells) can be dispelled, but there are exceptions as noted in individual spell and ability descriptions. Of particular note, most feats that do not duplicate a spell cannot have their effects dispelled (e.g. wild shape).

[edit] Dispel check

When a dispel attempt is made, a dispel check is performed. The factors affecting this check are the levels of the casters involved (i.e., the caster who is trying to dispel and the caster of the effect being dispelled). The exact check is

1d20 + dispel's caster level  vs.  11 + effect's caster level.

Ties indicate the effect is destroyed. Thus, there is a 50-50 chance of success when both casters have the same level. Note, though, that most of the spells in the dispel line place a cap on the dispel's caster level.