You know when you cast a spell and you lose concentration? That's a miscast.
Why don't we flesh out this more, giving a bit more of life to the mud. By introducing miscast effects.
Something akin to the perils of the Warp for 40K warhammer, or Dungeon Crawl Stone Soup magical contamination.
On warhammer, most times you "cast a spell" you have to roll a dice, and if you roll a certain range you have to roll on a special table where bad stuff happens. Most of it cosmetic, but others deadly.
On Dungeon Crawl Stone Soup every time you cast you start to get magical contamination, akin to radiation contamination. When you miscast you get a lot of of it, and a chance for bad things to happen.
As your magical contamination grows, you will start to glow impairing stealth and you might stat to mutate and gain bad/good mutations (horns, scales, antennas, weakness, ...).
Most of this stuff would be to hard for FL, because we have to train spells by spamming them many times, so there should not be "perils" or deadly stuff. At least I don't see a way for them to exist and a character not die from training.
BUT there is no reason why we could not have cosmetically effects for miscast. Emotes, room emotes, perhaps even area emotes.
Stuff like:
You lose concentration.
The air around you suddenly turn ice cold.
A soul chilling scream can be heard from the beyond.
Suddenly the dust and small pebbles start to float upwards before falling down again.
You feel as if some force has taken an interest on you.
You feel as if someone is observing you.
Your hands start to briefly glow.
The room flares blue in arcane light.
The room flares in blindingly bright neon light.
You body starts to emit a sickly glow and it's suddenly gone.
We could even perhaps add the magical glow thing. And have after you accumulate a certain number of miscasts the character glow. Like with faerie fire/fog.
We could try to do perils bad stuff, and bypass training by creating a ring that decreases HP heavily but increases managain and blocks miscast effects. And perhaps protect sub 30 from bad stuff. Or limit bad stuff to pinnacle. But I have a impression the Pbase would not like being forced to train with a ring or have bad stuff happen because they lost concentration in PK.