I saw a few posts from around summer talking about some sort of ‘Butterfly Trend’

What was/is it?

I think it was just a bunch of people that changed their PFP's to the butterfly from Scratch's art library.

Users once decided to create a “butterfly church” to glorify the butterfly sprite. Now, the trend is pretty much dead.

Oh boy, I can definitely answer this question, because I kind of started it.

I created a studio called “the butterfly cult” about the butterfly from the sprite library because of a funny post made by garnetluvcookie in a suggestion about making Scratch more mature (here it is) and a lot of people joined. We all said how great the butterfly was, and we said “glory to butterfly” often. We also changed our profile pictures to the butterfly.

Also, the wiki says “a group of forum helpers”, but that's not really accurate.

There was this thing where the butterfly was supposed to give out some sort of sweet - I think donuts - every Thursday to all its followers.

You might learn some things by checking out those users the Wiki provides as references for joke accounts.

The butterfly had an evil twin with a red eye.

The original studio “the butterfly cult” was at https://scratch.mit.edu/studios/26871465/ but it no longer exists.

A schism occurred soon after the original studio was created by Mr_PenguinAlex.

Some credited the start of the trend to @garnetluvcookie, and they created “The Butterfly Church”

That studio still exists at https://scratch.mit.edu/studios/26891479/

The goal of the butterfly cult was to get on the Scratch Trends wiki page. After doing so, I said “the butterfly's reign is over” and deleted the studio.
Then after a while, I remade the studio, but at that point the trend had died and the joke wasn't funny anymore, so I deleted that studio as well.

These are the three joke accounts referenced:

@butterfly-lord: made for the butterfly cult; it represented the good butterfly

@butterfly-creator: made for the butterfly cult, and then used in The Butterfly Church more often; this represented the first/oldest of many good butterflies (the butterfly cult strictly discussed the existence of one butterfly, while The Butterfly Church at times discussed many butterflies altogether)

@krakblee; made for the butterfly cult; this was an enemy, the bad butterfly, the good butterfly's evil twin; named after a comment (I forget by who) told the world that the butterfly had an evil brother

mlcreater wrote:

These are the three joke accounts referenced:

@butterfly-lord: made for the butterfly cult; it represented the good butterfly

@butterfly-creator: made for the butterfly cult, and then used in The Butterfly Church more often; this represented the first/oldest of many good butterflies (the butterfly cult strictly discussed the existence of one butterfly, while The Butterfly Church at times discussed many butterflies altogether)

@krakblee; made for the butterfly cult; this was an enemy, the bad butterfly, the good butterfly's evil twin; named after a comment (I forget by who) told the world that the butterfly had an evil brother

I didn't know about krakblee, I don't think they ever made a comment on the studio.