Honestly, don't know why this asinine prebuffing needs to take place. Just have it be an option that can be activated during the dialogue, just have the option show you how many spell charges you have remaining. But having to preemptively prepare these spells on a target or yourself before dialogue feels so tedious. The amount of time I've spent casting Guidance on myself throughout the game before saving to be ready to reload if the dice roll fails is starting to wear on me.
