End Grid Islands

Grid islands are a part of the outer islands of the End. A single island represents a random area of a world, and will spawn the same mobs as that area would. If connected to a part of a structure, it will also spawn mobs that only spawn once in the generation of that structure. For example, it would sometimes spawn evokers if connected to a woonland mansion or shulkers if connected to an End City. If the area they'd been connected to has a structure within 10 chunks, it will be connected there instead.

Or, it could be connected to a shrine, which if any mob were to enter an enderman would pick them up(or just get teleported automatically) and put them on the connected island. It's only one way, unless a player drops a stack of ender pearls as an offering(or maybe by placing a Bismuth Gift block, a block that I suggested) in which the player will be teleported back to the shrine. The Grid Islands could have a "Grid Core" block, which could be placed anywhere else in the outer islands along with some End stone in the shape similar to a Grid Island to allow direct transport between the Overworld and the outer islands.

Bismuth Gift block: https://feedback.minecraft.net/hc/en-us/community/posts/4404928239117-Ender-Bismuth