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I would probably make spells easier to interrupt like they were in 3e.
https://www.d20srd.org/srd/magicOverview/castingSpells.htm
These two things were key:
- Casting a spell provokes an opportunity attack
- Taking any damage requires a check or you lose the spell
Now casting when the orc warlord is up in your face is a lot riskier.
I think I get why they got rid of this system. It was more to think about, and I think they wanted the game to generally be easier so more players could enjoy it. Certain classes of player don’t want to think about tactics and positioning. They want to cast fireball. But as a result, the whole game is kind of shallower sometimes.
For mages countering mages, I’d probably give it a rework. It shouldn’t just be its own spell. It should be an action. Maybe have a separate check to identify the spell, or maybe just tell the player to skip double rolls. Then make some sort of opposed check. Use the spell level delta (and if you had them roll to identify, how thematically opposite the spell is. Like a fire and ice spell, or shield v magic missile).
An advanced technique: ask your players to make shit up.
Like, the players decided to go to the wizard university the wizard PC graduated from. So I ask him, “what’s their entrance hall like?” and let him just riff on it for a while. Players feel more engaged with the world, and it’s a little less work for me.
Warlock is trying to commune with his patron. I ask, “what is your patron usually like?” and the player is delighted to describe “the great sculpin” in detail. This then inspires me further.
Note that some players are very much “just tell me a story” and don’t want any input, and won’t like this. Some players are also shy and don’t think well on their feet. And some players are just really bad at staying on theme. But if you know your players , this can be a powerful technique.