BG1: TotS, BG2, BG2: ToB, IWD, IWD:HoW, IWD:TotL

This file format describes an effect (opcode) and its parameters. The format is an extended version of that found embedded in creatures, items and spells, and is a replacement for the version 1 embedded effects used in BG1. The engine appears to roll a probability for each valid target type, rather than one probability per attack.

Overall structure:

Offset	Size (data type)	Description
0x0000	4 (char array)	Signature ('EFF ')
0x0004	4 (char array)	Version ('V2.0')

When an effect is called via an eff, several of the fields (including duration and timing mode) are overriden by the calling SPL/ITM. Other fields are copied directly from the calling SPL/ITEM and overwrite the values defined in the EFF.

Offset	Size (data type)	Description
0x0008	4 (char array)	External EFFs - the field is the same as the signature field from the header Embedded EFFs - this field is zeroed out
0x000c	4 (char array)	External EFFs - the field is the same as the version field from the header Embedded EFFs - this field is zeroed out
0x0010	4 (dword)	Opcode number
0x0014	4 (dword)	Target type 0=None 1=Self (pre-projectile) 2=Pre-target 3=Party 4=Everyone (inc. party) 5=Everyone (excl. party) 6=Everyone matching specific value of caster (or Party if cast by party member) 7=Everyone matching specific value of target 8=Everyone (excl. caster) 9=Self (post-projectile)
0x0018	4 (dword)	Power
0x001c	4 (dword)	Parameter 1
0x0020	4 (dword)	Parameter 2
0x0024	2 (word)	Timing mode 0=Duration 1=Permanent 2=While equipped 3=Delayed Duration 4=Delayed 5=Delayed (transforms to 8) 6=Duration? 7=Permanent? 8=Permanent (unsaved) 9=Permanent (after Death) 10=Trigger 4096=Absolute duration
0x0026	2 (word)	Timing ?
0x0028	4 (dword)	Duration
0x002c	2 (word)	Probability 1
0x002e	2 (word)	Probability 2 Note: The BG1 engine treats probability as a single word, effects are applied in the range 0-probability. Note: Other engines treat probability as two values, effects are applied in the range probability <= x <= probability. Probability range is 0-99
0x0030	8 (resref)	Resource
0x0038	4 (dword)	Dice Thrown
0x003c	4 (dword)	Dice Sides
0x0040	4 (dword)	Saving throw type bit 0: Spells bit 1: Breath bit 2: Death bit 3: Wands bit 4: Polymorph NB. If more than 1 saving throw type is specified, the target rolls against their best save
0x0044	4 (dword)	Save bonus
0x0048	4 (dword)	Set local variable only if non-existant
0x004c	4 (dword)	Primary type (school)
0x0050	4 (dword)	Unknown
0x0054	4 (dword)	Parent resource lowest affected level
0x0058	4 (dword)	Parent resource highest affected level
0x005c	4 (dword)	Resistance The default behaviour is that effects cannot be dispelled and ignore resistance. bit 0: Can be dispelled, affected by resistance bit 1: Ignores resistance (when used in combination with bit 0) This can also be presented in the more traditional way: 0=Nonmagical 1=Can be dispelled/Affected by resistance 2=Cannot be dispelled/Ignores resistance 3=Can be dispelled/Ignores resistance
0x0060	4 (dword)	Parameter 3
0x0064	4 (dword)	Parameter 4
0x0068	8 (resref)	Resource 2
0x0070	8 (resref)	Parameter 5 (VVC) (aka Resource 3)
0x0078	4 (dword)	Unknown
0x007c	4 (dword)	Unknown
0x0080	4 (dword)	Caster X coordinate
0x0084	4 (dword)	Caster Y coordinate
0x0088	4 (dword)	Target X coordinate
0x008c	4 (dword)	Target Y coordinate
0x0090	4 (dword)	Parent resource type (0=None, 1=Spell, 2=Item)
0x0094	8 (resref)	Parent resource
0x009c	4 (dword)	Parent resource flags (from SPL 0x18 or ITM ext header 0x26)
0x00a0	4 (dword)	Projectile
0x00a4	4 (dword)	Parent resource slot
0x00a8	32 (bytes)	Variable
0x00c8	4 (dword)	Caster level
0x00cc	4 (dword)	FirstApply (internal flag)
0x00d0	4 (dword)	Secondary Type
0x00d4	4*15 (dword)	Unknown