These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Fridge Brilliance: Waver Velvet and Rider had a rough relationship during the Fourth Grail War, but ultimately bonded and became such good friends that they'd have no problem working together in the Fifth. So Waver gets a second Servant, Genghis Khan, who is not only a complete stranger, but also similar enough in personality to Iskander to start a rivalry with him on the spot, causing him to start acting out all over again as well, as well as driving Waver up the wall himself. Here We Go Again!
Once again, Waver did not know what he was getting himself into with the Grail War.
Lancelot's airplane flying skills. On one hand, it's a reference to his airborne dogfight with Gilgamesh in Fate/Zero. On the other hand, his piloting skills come from Knight of Honor, which only grants him proficiency with it as a weapon, hence why he has to fly it like he is in a dogfight, because that is the only way his Knight of Honor ability would allow him to fly.
Hilariousin Hindsight / Getting Crap Past the Radar: When Shirou asked Extra Saber to wear something more decent out in public, she chose her bride outfit. Which Shirou reluctantly okay'd as long as she zipped it up. Then came CCC and it shows that the outfit has an ass crack window. So instead of letting them see the front, she's letting them see the back.
Les Yay: See Funny Background Event above. On one occasion Nero wakes up in a compromising position with Saber... and decides that it's actually quite comfortable, and she'd like to stay there a little longer.