Caius Cosades, everyone's favourite stim-huffing ripped-as-shit 'Uncle', is the Grand Spymaster of the Blades, and an Imperial Monk, which is absolutely nothing to scoff at. Man has some seriously powerful magicka on tap, aside from the fact that he can most likely invert you with his bare fists.
But you never... Really even get a hint of that, y'know? He's just there. He's a trainer, sure, but he's just there, then he's gone later.
I had an idea for a fun little mod that'd just hammer that home without needing to do anything drastic, like put him in combat or whatever.
I'd love it if, after doing one or two of the early '[X] Informant' quests, you come back to Caius' place to see the aftermath of a short, vicious battle, with Caius completely unphased and unchanged, and you can determine roughly what happened by the state of the room, what items are on the bodies, and where the bodies are in the room.
As an example, I imagine some stars or darts stuck in walls opposite the door, toward his bed. The first body is crumpled right at the doorway, and the little nightstand usually next to his bed is scattered near the door, with blood on it. A depleted jinkblade is stuck in the ceiling, smacked out of the grasp of the second assailant, whose body lies under a hastily thrown wall-tapestry - inspection of the body indicates the head is facing entirely the wrong way (might need some model trickery/movie magic illusions here to make the visual correct.) Carbon scoring on adjacent walls indicate some spells thrown from the third assailant, slumped atop the storage chest in his room. There are dark, irregular blood splatters on the wall next to the door above a few piles of bonemeal, and sticking out of each eye socket of the slumped mage are two large, snapped, bloodied bones - similar to those that protrude from Bonewalkers.
Caius makes brief mention of this if you ask about 'what happened here', saying something along the lines of 'a bunch of fools trying to part an old man and his sugar, while he slept, no less! They expected a scrib - they found a warrior. I know you probably want to tell me how your meeting with the Informant went, but I can't be seen dumping these bodies, so I'll have to get rid of them in a way more amenable to... Local traditions. Do me a favour and pick them clean. They won't be needing their equipment.'
And, they don't have to really have anything great on them - Morrowind is king of not needing to drip feed the player character equipment - so long as they're not rocking full glass/dwemer/daedric, then it's actually better immersion to give them lore-appropriate equipment for their fighting styles and such.
And then when you come back after a day has passed, the place is as it was before.
Just something small and fun, enough to get a very clear understanding that Caius made it to where he is for a reason, and it might not be just the moonsugar.