Woah, someone actually giving tactical advice on these forums! I can safely retire now!
If you have that component installed, you can also use spell thrust, secret word or ruby ray to remove his SI.
Seeing how Ruby Ray is from a different school than ST and SW, you can cycle between these to counter those infamous double-immunity combo's that you sometimes see in mods. (Undead Sola comes to mind)
Lastly, scroll-cast spells as well as those from contingencies ignore invisibility.
[url="http://www.gamebanshee.com/forums/baldurs-gate-ii-shadows-of-amn-9/guide-to-tactical-mods-spoilers-116063.html#post1068546"]BG2 tactical mods guide[/url]
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