From 105e forward these effects are automatically done when someone enters an area for first time:

Prefix the tag of your object with “mfx” and the characters of the effects or colors you want, followed by an underscore “_”.

Effect codes:

• S Stone (VFX_DUR_PROT_STONESKIN)
• W Wood (VFX_DUR_PROT_BARKSKIN)
• D Dark (VFX_DUR_PROT_SHADOW_ARMOR)
• B Blur (VFX_DUR_BLUR)
• T Tentacles (VFX_DUR_TENTACLE)
• L Leaves (VFX_DUR_ENTANGLE)
• X webs (VFX_DUR_WEB)
• E Ethereal (VFX_DUR_ETHEREAL_VISAGE)
• A Anti-Light (VFX_DUR_ANTI_LIGHT_10)
• I Invisibility (VFX_DUR_INVISIBILITY)

c colored light (do cx#, where x is a the color code, and # is the intensity 1 to 4)

• b blue
• g grey
• o orange
• p purple
• r red
• w white
• y yellow

If the effect is permanent, leave the MFX_DURATION local float for the object as 0.0f (or just don't define the variable). Otherwise for an actual duration, set the MFX_DURATION local float for that object to a positive value.

If you want to do things like fill pits in area with water or lava. Or to cause a gradd covering or something.. these are the steps to take:

Make sure you use the standard onenter script in the area (_gen_oneneter)

Place variable int:
TileFill0 to a nonzero value for a non fire and forget VFX
Set.
set float TileHeight0 to height of tilemagic effect. -1.5 is usually good for pits of water. 0.2 good for covering the groundlevel.

if you want whole area to be filled, no further action is needed, but if only part set following variables:
TileStartX0 Start X location
TileStartY0 Start Y location
TileEndX0 End X location
TileEndY0 End Y location

if you need many effects, make TileFill1 as next and so on.

normal tilemagic things to use as values for TileFill
a full list of possibilites, though most will probably not look good…

Setting TileFill0 to negative value will cause an essence stream instead