In BG1, the god-spell was lightning bolt. That thing could easily be an insta-kill, and you can't dodge it (lots of fun bouncing around with cheats and seeing the bolt just change direction mid-air to houd you once again).
I did tons of mucking around in the early stages of the game, making a new character and trying to kill everyone in Candlekeep. The guards are seriously tough, and can easily be your doom if you meet more than one at a time. But the real threat is the courtyard. There's a mage in there (not Gorion, he's a pansy) who will cast lightning bolt at you as his first move. For such an early-level char, that pretty much spells your death sentence unless the RNG gods smile on you and roll a minimal amount of damage. Still though, that pretty much takes out all your health, and he's got five more bolts where that one came from.
Elminster, if I remember correctly, pretty much just casts stoneskin and then starts whacking you with a stick. The only reason this works is because he can't actually be killed. Trust me, I've tried. Several times.
Ahh, imprisonment... That spell was sick. Near-instant cast time, no saving throw, no resistance, no nothing. Not a damn thing you can do except hope someone can cast freedom.
Or reload from a previous save if you're playing singleplayer. God damn that was lame...