Effects (aka opcodes) are one of the main methods of affecting creatures in the IE, and are used in spells and items. Different effects are implemented in each revision of the IE, though several effects are common to two or more revisions (though the effects may work slightly differently). Effects typically have several parameters, including a timing mode (i.e the length of the time effect should remain active), a resource key (to reference another file) and a target type (to indicate which creatures to affect). Not all effects respect all parameters.

Each revision of the IE implements different effects. The list of effects for a specific revision of the IE is often increased by any expansion packs for the actual game (e.g. BG2 : ToB adds several new effects to BG2 : SoA). The number of effects available in each revision of the IE is presented below.

Engine revision	Start effect	End effect	Notes
BG1	0	175
BG1 : TotS	0	191
BG2 : SoA	0	297
BG2: ToB	0	317
BG(2): EE	0	367	Since game patch 2.0
PST	0	212
IWD1	0	265
IWD1 : HoW	0	???
IWD1 : TotL	0	296
IWD2	0	457	Effects 299 to 399 do not exist

BG1
BG2
BG(2)EE
IWD1
IWD2
PST