Better on DVD: The Manga volumes have redrawn scenes from the original serialization that make the characters look more consistent.
Defictionalization: The Lunarian puppy plushies Red Beryl makes for Diamond and the other gems are real toys that can actually be purposed, at least on eBay.
Dueling Works: Tends to be seen as this with Steven Universe, especially once the anime adaptation started. This is a bit strange, since they have few similarities, other than the basic concept of humanoid beings made of gemstones (Lustrous is a seinenCGI manga/anime loaded with Mind Screw and Buddhist imagery, Steven is a traditionally-animated American adventure story with a Kid Hero and musical numbers).
Phos post getting Lapis' head is usually called "LaPhos".
Cairngorm gets all sorts of silly nicknames to mispronounce their name. "Craig" is most common. "Butterfly" or "Mooncake" became popular alternate nicknames for Cairngorm after they get their eyes replaced, at least on 4chan threads. "Karen" also became popular.
Prayer involving not just Lunarian destruction, but also involving the Lustrous was a commonly held theory before its reveal in Chapter 80. There was also a lot of speculation over Sensei holding off on it not out of duty, but of love for the Gems he raised.
Cue a lot of fans saying they called it when Chapters 79 and 80 revealed that the Lunarians would never hold up their end of the deal with Phos. The Lustrous revival project stopped immediately after Phos gets shelved, and once the Gem is able to make Sensei pray Aechmea revealed that the action would wipe out all of the humanity subspecies.
International Coproduction: Not the series, but the Latin American Spanish dub, as it was done with voice actors from both Argentina and Chile, both neighboring countries, and just like with the No Game No Life Zero movie dub, this is one of the few dubbing co-productions which doesn't feature either Mexicans or Hispanic voice actors from the U.S. Also, this is the first Sentai Filmworks' non-English dub.
What Could Have Been: The first preview for the anime was entirely in 2D animation, implying that the series wasn't actually going to animated in 3D.