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2) Weaken casters
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I've been thinking about this a bunch the past few days. Some spells could be seriously tweaked down by making them either more ritualistic in nature, longer casting times, concentration to maintain, longer periods of time before the spell takes effect... etc. Basically making useless for spur of the moment combat casting.
I've been working on some 3.5 house rules lately, and switching how spells work is part of it. Admittedly, it's a very quick and crude patch, but it might help a bit. It was more of an effort to make different types of spells be on par with each other. Basically, it goes like this (I go into a bit more detail in the actual rules):
Save or Die:Increase casting time to an entire round (not a full-round action), similar to Sleep and the Summon Monster spells. The advantage is it gives people time to react, and the caster has to consider if it's worth trying to cast. Also, I like the cinematic concept of the caster ominously chanting while everyone either runs for cover or desperately tries to get past the fighter and stop him.
Save or Lose:These are categorized as spells that deal a laundry list of conditions (such as blinded, stunnded, and nauseated), spells that lower your movement to half or less, and spells that completely trivialize your actions (like Baleful Polymorph). These are cast as full-round actions. You can still fire them off in one round, but you can't also move. Makes it a little harder to set up Color Spray at low levels.
Direct Damage:These get boosts to damage based on the spell level and an additional rider effect based on the damage type (catch on fire for [fire], Str-based penalties for [cold], Dex-based penalties for [electric], etc).
Again, this doesn't even come close to bridging the gap between casters and non-casters, but I'm curious to see how it works in practice. I think a full approach would sadly include re-writing most of the spells from scratch.