I am interested in Scratch trend activities because I like to customise them. I have found some trends that are NOT on the list, but I may need your help to find more.
Project Trends
Usercards
Usercards are projects that follow the format “This user ______” mainly for joking or to spread a cause. This is an example of a usercard.
Coffin Dance
Many users make Coffin Dance projects that show people holding a coffin with the “Coffin Dance” song.
Studio Trends
One Project Advertisements
Some studios have one project only and is used for advertising it. The maker of the project will invite every follower to join the studio. Adding projects is usually not allowed in these studios.
____ Research
These studios claim to “do research” on the history of mysterious users like kaj.
Forum Trends
Role|Achievement|Interest Signature Formats
In many signatures, a user’s roles, achievements or interests appear and are separated by vertical bars like:
Scratcher|Writer|Astrophysics Lover|Art|Scratch Wiki|Currently Learning Calculus
Profile Trends
Unshared Featured Projects
Many people use unshared projects as their featured projects with multiple tabs. The project is usually the user’s statistics, or a banner with their username on it.
That’s all I found! If you have noticed any more trends, please post here!

Because trends always come and go, so the wiki users forget about them, and some of these are not trends

SciBlazeMaker wrote:

Generic Platformers
Generic platformers are games that have a square player to jump through obstacles. The player can jump on walls and is immortal. There are spikes and lava in the game. Generic platformers are controversial because they are not creative.

This is not a trend, it’s a type of project that always existed

One Project Advertisements
Some studios have one project only and is used for advertising it. The maker of the project will invite every follower to join the studio. Adding projects is usually not allowed in these studios.
____ Research
These studios claim to “do research” on the history of mysterious users like kaj.

Again, i don’t think these are trends, just types of studios, but i’m not too sure on this one

Snipping
When a user quotes a post and finds content that is not useful, they replace it with “snip” or something like that.

This isn’t a trend, it’s basic forum stuff. Saying that snippin is a trend is like saying that bumping is a trend

OC Profile Pictures
Some people create an OC (original character) that represents them in projects, or even claim they are the OC. Many people use an OC for a profile picture.

OC’s always existed, it’s very generic, since OC’s can be anything you want and don’t resemble each other, so i don’t think this counts as a trend.
The rest of the trends i didn’t quote i do think are trends

But a trend you should add is the “evil Kumquat” trend started by@cheddargirl

The evil kumquats trend is already in the wiki. It even has its main page: Evil Kumquat
I’ve updated the main post and now some of the “trends” that are not trends are no longer on it.

some of these are memes, which technically you could say they're scratch trends but they appeared everywhere

Most of the trends that you listed aren't very well known; we discuss them before adding them to the page. If you really think something should be on the trends article, you can suggest it in the Community Portal on the forums.

-Valtren- wrote:

some of these are memes, which technically you could say they're scratch trends but they appeared everywhere

If a meme is popular enough on scratch, it’s a scratch trend. Meme man is on the wiki page, and it’s a meme

KangaCoder wrote:

Most of the trends that you listed aren't very well known; we discuss them before adding them to the page. If you really think something should be on the trends article, you can suggest it in the Community Portal on the forums.

Yeah, i agree (except with the coffin dance).

But, Scratch Wiki also has a trend that exists not only on Scratch but everywhere, which is rickrolling. Forum Trends (Rickrolling)

SciBlazeMaker wrote:

But, Scratch Wiki also has a trend that exists not only on Scratch but everywhere, which is rickrolling. Forum Trends (Rickrolling)

Right - because rickrolling occurred quite often, especially in the forums, so it was added.

By the way, is there a legit way to start a trend or does it require serendipity to create a new trend while following the rules of Scratch?

SciBlazeMaker wrote:

By the way, is there a legit way to start a trend or does it require serendipity to create a new trend while following the rules of Scratch?

Trends are pretty much serendipitous things - very rarely has a trend started with the intent to be a trend. Most of it is random luck (but I guess in the case with the Evil Kumquat, stuff the ST posts has a tendency to take a life of its own at times).

A while back Goboified remixes were popular (taking a project and replacing a lot of it with Gobo).

I think wiki editors try to make sure they're not letting quick, lesser-known trends clog up the page. They're probably prioritizing trends that are popular across much of the site or the forums.