Myren Eario | Falling End Portal Line Placer @myreneario7216 | Uploaded 2 years ago | Updated 4 hours ago
This contraption was not made by me, but by Skye (Discord tag: Skye#5069). This video just showcases their contraption.

The contraption uses a single falling end portal entity to place down a line of end portal blocks near overworld spawn.
Whenever the falling end portal is placed down, we use the previously placed end portal block to duplicate it and keep it alive for the next step.
One could also make a more advanced version of this contraption that uses the end portal line to place down and dupe a line of another falling block.
If this kind of technology gets developed further, then it can be used to fill perimeters with command blocks or make an eol enderman farm by spamming nether portals in the end.

Currently the contraption gets very slow very quickly, because the falling end portal has to be repeatedly transported from overworld spawn to the flying machine.
The transportation could be made much faster by using tnt cannons.
If the following two bugs get fixed, then one can also make a fast falling block placer by using end gateways:
bugs.mojang.com/browse/MC-254004
bugs.mojang.com/browse/MC-9644
So go and upvote those bug reports!
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World Download: mediafire.com/file/un0eth9yt0u8mx2/End+Portal+Line+Placer+by+Skye.zip/file

The world download also includes litematics for the overworld and end part of the contraption.
In the overworld part there is a red concrete block that needs to be aligned with the spawn point. The end part needs to be aligned with the obsidian platform.

The video was recorded in version 1.18.2. It should also work in many other versions.
The contraption requires the end to be loaded. In the video I use a carpet bot for that.
I also used a command block to once summon in a falling end portal. In survival you of course have to get the falling end portal in 1.12 and then upgrade your world.

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If this video confuses you, then you can watch this as a prerequisite: youtube.com/watch?v=l9aw_Db_4q4